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Mam  Lib. 


SUBMAIIINE     MINES 

AND 

TORPEDOES 

AS   APPLIED    TO   HARBOUR   DEFENCE. 


SUBMARINE    MINES 

AND 

TORPEDOES 

AS  APPLIED  TO  HARBOUR  DEFENCE. 

BY 

JOHN   TOWNSEND   BUCKNILL, 

Honorary  Lieutenant-Colonel  (Late  Major  R.E.),  Reserve  of  Officers. 

Formerly  (from  1873  to  1886) 

"■  R.E.  Secretary  for  Experiments  ;'^  "■Member  and  Secretary''^  of  the  "-Joint   War 

Office  and  Admiralty  Committee  on  Experiments  against  H.M.S.  '  Oberon  ;'  " 

"  Secretary  "  of  the  yd  "  War  Office  To7-pedo  Committee  ;^^ 

''Assist.  Instructor  for  Submarine  Mining,^^  School  of  Military  Engineering,  Chatham. 

Submarine  Mining  Officer  at  Woolwich. 

Ear  some  time  acting  "  Inspector  Submarine  Defences  "  at  the  War  Office  ; 

''Executive  Officer  for  Submarine  Mining  in  the  Southern  District.'''' 

AUTHOR    OF    "torpedoes   VERSUS    HEAVY    ARTILLERY,"    1872, 
"  PROTECTION   OF    BUILDINGS    FROM    LIGHTNING,"    1S81, 


Reprinted  and  Revised  from  "Engineering." 


NEW   YORK: 

JOHN    WILEY    &    SONS, 

15  AsTOR  Place. 

LONDON:   OFFICES    OF  "ENGINEERING,"   35  &  36    BEDFORD    ST. 


^^ 


PEEFACE. 


IN  this  hook-producing  age,  the  man  who  writes  one  owes  an 
apology  to  the  puhlic. 

The  following  pages  have,  for  the  most  part,  already  appeared 
in  Engineering,  in  a  series  of  articles  on  submarine  mining,  and 
several  requests  having  been  received  to  repul)lish  same  in  book 
form,  it  has  been  determined  to  do  so. 

An  examination  of  the  Table  of  Contents  enables  a  reader  to 
separate  theory  from  practice.  The  general  sequence  of  the 
chapters  has  been  arranged  as  far  as  possible  in  the  order  in 
which  a  scientific  subject  should  be  investigated,  viz.:  (1)  Theory  ; 
(2)  Experiment;  (3)  Practical  Application.  In  compiling  these 
pages,  great  care  has  been  taken  to  guard  all  Government  secrets 
— those  arrangements  only  being  described  which  have  already 
been  published,  either  in  the  specifications  obtainable  at  the 
Patent  Office,  or  in  the  public  press,  or  in  books  sold  to  the  public 
in  this  and  other  countries.  I  shall  feel  compensated  for  a  lono- 
year  of  labour  if  the  general  ideas  propounded  receive  attention, 
and  should  they  be  accepted,  I  shall  feel  that  it  is  more  due  to 
the  exceptional  advantage  of  having  worked  for  several  years  in 
daily  contact  with  the  English  Vauban  than  to  any  perspicuity 
of  my  own.  The  broad  principles  of  scattering  submarine  mines 
as  much  as  possible  should  be  identified  with  him  (Sir  Wm.  F. 
Drummond  Jervois),  and  if  he  agree  in  the  main  with  the 
contents  of  the  following  pages  I  shall  consider  their  accuracy 
proven. 

The  three  concluding  chapters  on  Torpedoes  will  enable  the 
reader  to  form  an  opinion  as  to  the  value  of  these  weapons  for 
harbour  defence,  and  as  to  the  manner  in  which  they  can  best  be 
employed  in  conjunction  with  other  arms.  General  Abbot's  excel- 
lent work  on  "  Experiments  with  Submarine  Mines  in  the  United 
States  "  has  been  of  the  greatest  assistance,  although  I  have  taken 


exception  to  soinc  of  his  deductions.  Many  other  authorities  have 
been  quoted  and  are  duly  acknowledged  in  the  text.  My  own 
inventions  connected  with  submarine  mining  are  perhaps  noticed 
too  prominently,  but  it  was  necessary  to  illustrate  the  various 
and  necessary  contrivances  by  some  special  patterns,  and  it  not 
unfrequently  occurred  that  I  was  compelled  to  describe  my  own 
patterns  or  none  at  all,  the  Government  gear  being  treated  as 
secret  and  confidential. 

For  a  similar  reason,  it  being  impossible  to  indicate  the  defects 
of  our  service  arrangements  with  precision,  I  have  been  com- 
pelled to  attack  their  intricacy  in  general  terms  only. 

On  matters  connected  with  the  'personnel  and  the  purchase  of 
stores,  however,  it  has  been  possible  to  go  into  detail ;  and  if 
some  of  the  remarks  appear  to  be  harsh,  my  excuse  must  be  that 
the  subjects  required  it.  Minced  language  is  not  a  desirable 
form  of  expression  when  the  writer  believes  that  the  efficiency 
of  an  important  item  in  National  Defence  is  at  stake. 

J.  T.  B. 

Southampton,  Dec,  1888. 


A, 


-\ 


CONTENTS. 


CHAPTER  I.     (p.  1). 

Introductory  Remarks — Results  obtained  during  American  War  of 

Secession,  and  by  Experiments. 

Analysis  of j  the  "  Oberon"  Experiments — Analysis  of  the  Carlskrona  Experiments 

— Analysis  of  Miscellaneous  Experiments — PormuljL'  for  Pressures  Produced. 

CHAPTER  II.     (p.  13). 
Apparatus  Employed  for  Measuring  the  Effects  of  Sueimarine  Explosions. 
Mud  Craters— Photographs — Rodman's  Gauge  Modified  by  King — Noble's  Gauge 
—  Frencli     and    Danish    Modifications    thereof  —  Ikicknill's  Tubular   Dyna- 
mometers. 

CHAPTER  III.  (p.  23). 
Theoretic  and  Empiric  Formula. 
English's  Theory — Abbot's  Theories  Examined — Abbot's  Conclusions  briclly 
Noted— Abbot's  and  English's  Theories  Compared — Detonating  Compounds 
and  Explosive  Mixtures — Characteristics  of  Same—  Considerations  Atiecting 
the  Thickness  and  Material  for  Mine  Cases,  also  the  Air  Spaces,  Methods  of 
Ignition,  &c. — Formulre  proposed  by  the  Author,  based  on  English's  Theory 
—Comparison  with  Abbot's  Formulae— The  Calculated  Pressures  from  each 
Plotted  Graphically. 

CHAPTER  IV.  (p.  41). 
Examination  of  Different  I]xpi,osives. 
Dynamite  —  GunCotton — Dualin  —  Lithofracteur  (Rendrock)  —  Giant  Powder — 
Vulcan  Powder — Mica  Powder— Nitro-Glycerine — Hercules  Powder— Electric 
Powder — Designolle  Powder — Brugcre  or  Picric  Powder — Tonite — Explosive 
and  Blasting  Gelatine — Atlas  Powder— Judson  Powder— Rackarock — Foreite 
Gelatine— Gelatine  Dynamite— Gelignite— Melenite—Roburite— Further  Re- 
marks on  the  most  Suitable  Explosives  for  Submarine  jSIining,  viz..  Dynamite, 
Gun-Cotton,  Tonite,  Blasting  Gelatine,  Forcitoand  (ielatine  Dynamite,  witli  a 
Table  of  Relative  Values. 

CHAPTER  V.  (p.  5.')). 
Considerations  Guiding  the  Size  and  Nature  of  Mine  Cases,  &c. 
Wooden  or  Cork  .Jackets  Condemned— Loss  of  Effect  due  to  Air  Space  in  Mine- 
Charge  in  a  Contact  Mine  should  be  the  Effective  Minimum — Strength  Re- 
quired for  a  Mine  Case— Calculations— Mines  on  Single  and  on  Double 
Moorings  Compared — Side  Pressure  due  to  Tidal  Currents — Fronde's  Forniuhv 
—Difficulties  Engendered  by  Rise  and  Fall  of  Tide— Major  Ruck's  System- 
Spacing  of  Electro-Contact  Mines — Dormant  Mines — Explosive  Link—  Manu- 
facture of  Cases. 


viii  CONTENTS. 

CHAPTER  VI.  (p.  77). 
Observation  Mines. 
French  System— English  System— American  System— Grouml  Mines  with  De- 
tached Cil-cuit-Closers— Ground  Mines  Fired  by  Observers  —  Interdepen- 
dence of  the  Striking  Distances  and  the  Size  of  the  Effective  Circles  for 
Observation- The  Charges  Recommended  for  Use— The  Cases  :  Shape,  Size, 
Material,  and  Thickness— Buoyant  Mines  Fired  by  Observers— Charge  and 
Cases  for  Same— Best  Explosive  for  these  Mines— Spacing. 

CHAPTER  VII.    (p.  89). 
Mooring  Geak. 
Sinkers— Necessary  Weights  Calculated— Table— Patterns  Recommended— Moor- 
ing Lines— Details  Concerning  Wire  Ropes  and  Chains— Shackles. 

CHAPTER  VIII.     (p.  101). 
Elkc'TKIC  Cables. 
Iklrltiple-Single  — Subterranean  — Covered  Wires   for   Shore   Stations— Electric 
Cables,  Conductor  of— Insulator— Core  Covering— Armouring— Preservative 
Compound— Dimensions  of  Finished  Cable— Shore  Ends— Crowns— Electrical 
Joints— Connecting  Boxes— Junction  Boxes— Cable  Entry  to  Mine. 

CHAPTER  IX.  (p.  109). 
Electric  Fuzes. 
High-Resistance  Fuzes— Brunton's  Fuze— Beardslee's  Fuze— Abel's  Fuze— Low- 
Resistance  Fuzes— Ward's  Fuze— Bucknill's  Fuze  — Fisher's  Fuze— American 
Service  Fuze -English  Service  Submarine  Fuzes— Theory  of  Lo-b -Resistance 
Fuzes— Abbot's  Safety  Formula— Disconnecting  Fuzes— Extremely  Sensitive 
Fuzes— Browne's  Compound  Fuze— Concluding  Remarks. 

CHAPTER  X.  (p.  119). 
Electrical  Arrangements  on  the  Mine  Fields. 
In  the  Mines,  Circuit-Closers,  &c.— Observation  Mines— Mines  with  Circuit- 
Closers— Armstrong's  Relay— Circuit-Closers  :  Austrian,  Abel's,  Mathieson's, 
Bucknill's,  McEvoy's— Wire  Entrances  to  Cases— Disconnecting  Arrange- 
ments for  Electro-Contact  Mines— Single  Disconnector— Multiple  Connector 
—Junction  Box  for  Electro-Contact  Mines. 

CHAPTER  XI.  (p.  132). 
Electrical  Arrangements  on  Shore. 
Electro-Contact  Mines— Firing  Battery— Mathieson's  Signalling  and  Firing  Appa- 
ratus—McEvoy's  Signalling  and  Firing  Apparatus— Apparatus  Fuze  Indi- 
cating—Advantages Claimed  for  Same— Rectifying  Paults— Electrical  Resist- 
ances of  Various  Woods— Firing  Observation  Mines  ;  by  Single  Observation- 
Charges  Required  under  Various  Conditions— Employment  of  Lines  of  Mines 
between  Maiks— Firing  by  Depression  Instruments— Defects  of  this  System- 
Command  Re<iuired— Command  Decreased  for  Mines  Fired  in  Pairs— Firing  by 
Double  Observation— Firing  Arcs— Plane  Table  Arrangements— A  New 
Method  Proposed- Various  Applications  of  Same— Conclusion. 

CHAPTER  XII.  (p.  154). 
The  Firing  ST.vrioN. 
Universal  Commutator— The  "  Earths  "—Insulated  Wire  for  Leads,  &c.— Testing 
the  Firing  Battery— Formula— Testing  other  Batteries— Formula— Testing  the 
Shutter  Apparatus— The  Sluitter  Adjustment- Testing  other  Instruments- 
Testing  for  Insulation- I n.struments  Proposed  for  this  and  for  General  Pur- 
poses—Sensitive Astatic  (ialvanometer— Megolini  Resistance— Testing  for 
insulation. 


CONTENTS.  ix 

CHAPTER  XIII.  (p.  163). 
The  Stoke  Dei-ot. 
Geaeral  Remarks  on  Storage— Wire  Ropes— Tripping  Chains —J  unction  and  Con- 
necting Boxes— Multiple  Connectors  and  Disconnectors — Mines — Apparatus 
—Priming  Charges— Fuzes— Sinkers— Battery  Cells— Instruments— Buoys- 
General  Stores— Consumable  Stores— Explosives-Boat  and  Steamer  Stores  — 
Boats  —  Electric  Cables  —  Cable  Barges  —  Cable  Tanks— Pier — Tramway  — 
Workshop— General  Plan  of  Depot — Position  of  Depot. 

CHAPTER  XIV.     (p.   168). 
Designs  for  Sea  Mining. 
General  Principles — Defence  of  Dockyards — Example  of  Advanced  Mines — Cher- 
bourg—Semi-Advanced  Mines— Mine    Blocks— Observation    versus  Contact 
Mines. 

CHAPTER  XV.     (p.   177). 
Designs  fok  Mine  Defence. 
General  Principles— Defence  of   Rivers   and  Commercial   Ports— Example,    New 
York— Scheme  of  Defence  for  Small  Coaling  Stations— Remarks  on  Defence 
of  Small  Harbours — Also  Open  Roadsteads  and  Coast  Towns- General  Con- 
clusion. 

CHAPTER  XVI.     (p.   187). 
Boat  and  Steamer  Equipment. 
Boats — Steam  Tugs  —Store  Lighters — Mooring  Steamers — Crew  and  Fittings. 

CHAPTER  XVII.     (p.   190). 
Practical  Work. 
Surveying  the  Mine  Field— Preparing  to  Lay  Mines— Connecting  up,  Embarking, 
and  Laying  Mines  and  Electric  Cables — Repairing  Faults. 

CHAPTER  XVIIL     (p.   196). 
The  Personnel  and  the  Stokes. 
Civilian  Personnel  Recommended  and  Compared  with  Military  Organisations — 
British  System  Criticised— Purchase  of  Stores — Government  Manufacture — 
The  Contract  System. 

CHAPTER  XIX.     (p.  203). 
Automatic  Mines. 
General  Remarks — Chief  Requirements — Chemical    Firing  Arrangements — Fric- 
tional— Percussive— Electrical— Mathieson's  System  Recommended  for  Har- 
bour Defence— Naval  Recjuirements  Differ — Mines  on  Frames  of  Timber  and 
on  Piles. 

CHAPTER  XX.  (p.  20!)). 
The  Attack  on  and  Defence  ok  Mined  Waters. 
Function  of  Heavy  Artillery— Attack  by  Small  Craft— Defence  by  ditto— Quick- 
firing  Guns — Smokeless  Powder — Function  of  Torpedo  Boats — Employment 
of  Local  Craft — Ci-eeping  for  Cables  made  Difficult — Sweeping  for  Mines — 
Countermining— British  System — Zalinski's  Proposal — Illumination  of  Har- 
bours— Electric  Lights — Reflectors — Lucigen  Lights — Obstructions — Nets — 
Booms — Boat  Mines — Cribs  of  Timber,  &c. 

CHAPTER   XXL     (p.  226). 
Torpedoes. 
Torpedo   Batteries— The    Whitehead— General   Description   of — Defects  of — The 
Howell  Torpedo — Detailed    Description    of — Comparison    with    the    White- 
head. 

b 


X  CONTENTS. 

CHAPTER  XXII.  (p.  233). 
Controllable  Torpedoes. 
Broarl  Distinctions  of  the  Benlan,  Lay,  Patrick,  Ericcson,  Sima-Edison,  Norden- 
felt,  and  Brennan  Torpedoes— The  Brennan— Description  of— Mode  of  Pro- 
pulsion—Steering— Observing  Course— Maintenance  of  Depth— The  Wire- 
Winding  Engine  —  Operation  of  Running— Speed— General  Remarks  on 
Brennan  Torpedo. 

CHAPTER  XXIII.  (p.  243). 
Torpedo  Artillery. 
Mefford's  Invention  Perfected  by  Captain  Zalinski,  U.8.  Artillery— Description 
of  the  Gun— Projectile— Electric  Fuze— Voltaic  Battery— Magneto-Electric 
Arrangement— Records  Showing  Accuracy  of  Range— Experiments  against 
Schooner  "  Silliman  "—Comparison  with  Controllable  Torpedoes— Proper 
Sphere  of  Action— Cannot  Replace  Mines. 


LIST    OF    DIAGRAMS. 


Fig.  1,  2,  3,  4,  p.  14.  American  Crusher  Gauges.     (King). 

,,  5,  6,  pp.  14,  15.  English  „  „  (Nobel). 

7,  p.  15.  French  ,,  ,, 

,  8,  p.  16.  Swedish  ,,  ,,  (Eckerman). 

9,  p.  l(j.  Pellet  showing  several  blows  from  one  explosion. 

"  10,  11,  12,  13,  t  rj,^j|_,^jjjj,j|y„,^^o^gtgrs.     (Author). 

14,  15,  p.  19.  ,,  ,,  in  cage  as  employed  under  water. 

','  lelp.  19.  Hydr'odynamic  apparatus,  for  testing  same. 

,',"  17,  p.  20.  Special  cage  for  testing  same. 

,,  18,  p.  24.  Illustrating  English's  theory. 

,,  19,  p.  38.  Results,  author's  formula,  shown  graphically. 

,,  20,  p.  39.  ,,       Abbot's        ,,  ,,  ., 

"  21'  2'^'Jl?'  2*'  I  Electro-contact  mines  and  ship's  side. 

p.  58.  J  1  •     11 

,,  25,  p.  61.  Steel  spheres.     Useful  facts  .shown  graphically. 

,,  26,  p.  64.  Buoyant  mines.     Single  and  double  moorings. 

,,  27, 28, 29, p. 70.    Rise  and  fall  mines.     (Ruck). 

„  30, 31, 32,  p.  70. 

,,  33,  34,  p.  70. 

,,  35,  36,  p.  73.       Dormant  mines.  ,, 

,,      37,  p.  74.  Explosive  link.     (Author). 

,,  38,  p.  75.  Electro-contact  mine,  spherical. 

',,      39,  p.  79.  Striking  distances.     Ground  mines. 

,,      40,  41,  p.  82.        Packing  gun-cotton  in  cylindrical  cases. 
',,      42,  p.  84.  Mooring  large  buoyant  mine  on  a  span. 

,,      43,  p.  90.  Action  of  a  buoyant  mine  on  a  sinker. 

',      44,  45,  p. 95.         Pattern  of  large  sinker.     (Author). 
,,      46,  47,  p.  96.  ,,  small      ,, 

"      *ro'*^'  ''lo'f^''  1  Connecting  and  junction  boxes. 
„      53.5'4,.55,p.lll.  Early  forms  of  low  resistance  electric  fuzes. 
,,      56,  p.  113.  English  service    ,,  ,,  denotator. 

,      57,  p.  121.  Testing  and  firing  apparatus,  early  form.    (Armstrong) 

,,      58,  p.  121.  Ball  and  string  circuit-closer  „  (Author). 

„      59,  p.  124.  „  „  „  new  pattern.        „ 


CONTENTS.  xi 

Fig.  60,  p.  12o.  Klectro-contact  mines  in  a  .striii". 

»  61,  p.  125.  ,,  „      on  fork. 

„  62,  p.  126.  New  form  of  circuit-closer.     Mechanical  retardation 

,,  63,  p.  129.  Single  disconnector.  UAiifhr.r^ 

„  64,  65,  p.  130.  Multiple  connector.  lU^umoi;. 

,,  66,  p.  LSI.  Junction  box  for  electro-contact  mines 

,,  67,  68,  p.  1.33.  Leclanche  cell. 

,,  69,  p.  134.  Signalling  and  firing  apparatus,  early  form.    (Matliicson). 

,,  70,  p.  137.  Fuze  indicating  apparatus.     (Author). 

,,  71,  p.  143.  Theory  of  depression  instruments. 

,,  72,  p.  144.  Error  in  ,, 

,,  73,  p.  147.  Fia-ing  by  intersection,  usual  method. 

,,  74,  p.  147.  ,,  ,,  for  advanced  mines. 

,,  75,  p.  150.  ,,        plane  table,  new  method.     (Author). 

,,  76,  p.  151.  Electric  switch  for  same.     (Author). 

,,  77,  p.  151.  Positive  and  negative  pulls  for  same.     (Autlior). 

,,  78,  p.  1.52.  Alternative  arrangement.     (Author). 

,,  79,  p.  153.  ,,  ,,  ,, 

,,  80,  p.  155.  Box  of  resistance  coils— firing  current. 

,,  81,  p.  161.  Method  of  taking  insulation  test. 

,,  82,  83,  p.  165.  llarge  for  storing  and  laying  electric  cables.      (Day   and 

,,  84,  p.  166.  Store  depot,  pier,  &c.  [Summers). 

,,  85,  p.  170.  Mine  defence  for  Cherbourg — example. 

,,  86,  p.  180.  ,,  „  New  York 

„  87,  p.  183. 

,,  88,  89,  p.  189.  Small  mooring  steamer.     (Day  and  Summers). 

,,  90,  p.  206.  Automatic  mine,  percussive  action.     (Author). 

,,  91,  p.  211.  Steamer  for  countermining,  &c.     (Zalinski). 

,,  92,  p.  213.  Electric  light  carriage,  long  and  short  range.     (Author). 

,,  93,  94,  pp.  214,  1 
215.  / 

,,  95,  p.  217.  Reflector,  silvered  glass.     Theoretical. 

,,  96,  97,  p.  221.  Boom  fitted  with  boat  mines.     (Author). 

„  98,  99,  p.  222. 

,,  100, 101,  p.  223. 

,,  102,  p.  229.  Howell  torpedo— elevation. 

,,  103,  104,  p.  229.         ,,  ,,  motor. 

„  105,  106,  107,  1  I,     •       ^  ,       , , 

p   230  f        "  "  horizontal  rudder,  control  of. 

,,  108,  p.  234.  Brennan  torpedo — sectional  elevation. 

„  109,  p.  234.  ,,  „  plan. 

,,  110,  p.  234.  ,,  ,,  cross-section. 

,,  111,  p.  235.  ,,  ,,  winding  engine. 

,,  112,  p.  236.  ,,  ,,  general  diagram. 

,,  113,  p.  237.  Whitehead  torpedo— level  gear. 

,,  114,  p.  24.5.  Torpedo  gun  in  emplacement. 

,,  115,  p.  246.  Electric  fuze  and  battery  for  projectile. 

,,  116,  p.  247.  Illustrating  experiments  with  schooner  Silliman. 


TABIvl' 

I., 

p- 

5. 

II., 

p- 

G. 

III., 

p- 

8. 

IV., 

p- 

10. 

v., 

p- 

10. 

VI., 

p- 

21. 

VII., 

p- 

22. 

VIII., 

p- 

22. 

IX., 

p- 

23. 

X. 

p- 

25. 

XI., 

p- 

31. 

XII. 

p- 

35. 

XIII. 

p- 

36. 

xtv. 

p- 

37. 

XV. 

p- 

37. 

XVI. 

p- 

39. 

XVII. 

p- 

40. 

XVIII. 

.  p 

4G. 

XIX. 

1  p 

54. 

XX. 

p- 

60. 

XXI. 

.  p 

67. 

XXII. 

.  p- 

77. 

XXIII. 

p 

77. 

XXIV. 

>  p- 

80. 

XXV 

.  p 

83. 

XXVI 

.  p 

.  86. 

XXVII 

>  p 

88. 

XXVIII 

.  p 

94. 

XXIX 

.  p 

98. 

XXX 

.  p 

99. 

XXXI 

,  p 

103. 

XXXII 

.  p 

139. 

XXXIII 

,  p 

216. 

XXXIV. 

.  I 

.216. 

CONTENTS. 
LIST    OF   TABLES. 


Abbot's  Analysis  of  Obei-on  Experiments. 

,,  ,,         Carlskrona  Experiments. 

J,  ,,         Miscellaneous        ,, 

Dimension  of  Vessels  in  Frencli  Experiments. 
Recommendations  from         ,,  ,, 

Tubular  Dynamometers  :  Experiments  withFalling  Weights. 
Eckermann's     Dynamometers  :      Experiments     with     Falling 

Weights. 
Noble's  Crusher  Gauges  :  Experiments  with  Falling  Weights. 
Englisli's  Examination  of  Same. 

,,  Comparison  with  Torpedo  Experiments. 

Explosive  Mixtures  Compared.       Abbot's  Formula. 
Author's  Formula.    Calculations  Compared  with  Experiments. 
Intensity  of  Action  of  Different  Explosives. 
Abbot's  and  Author's  Formuhe  Compared  with  Experiments. 
Effective  Striking  Distances  for  Charges  of  Different  Explo- 
sives Calculated  from  Author's  Formula. 
Ditto  Gelatine  and  Dynamite,  Abbot's  Formula. 

,,  I,  ,!         Author's        ,, 

Intensity  of  Action,  Explosive  Compounds,  Abbot. 
Relative  Values  of  Explosives  for  Submarine  Mining. 
Cases,  Spherical,  Steel  :  Useful  Facts. 

,,  ,,        Size  reiiuired  in  Different  Currents. 

Ground  Mines.     French  System. 

English      „ 
Striking  Distances  (ft.),  Different  Depths  (ft.)  giving  Effective 

Horizontal  Circles  (1)  30  ft.  Radius,  (2)  15  ft.  Radius. 
Cylindrical  Cases  for  Ground  Mines. 
Spherical  Cases  for  Large  Buoyant  Mines. 
Spacing  for  Large  Mines. 
Sinkers  required  under  Various  Conditions. 
Particulars  of  Wire  Ropes  for  Mooring  Lines. 

,,  Tripping  Chains. 

Dimensions,  Weights,  and  Resistances  o    Pure  Copper  Wires. 
]<]lectrical  Resistances  of  Woods  of  Sorts. 


Light  Reflected  from  Various  Surfaces. 
Eilciency  of  Glass  Mirrors,  Silvered  oc 


on  the  Back. 


FORMULA. 


PAOES. 

11,  28,  32.  Effect  of  explosions.     Abbot. 

11,  35,  36.  ,,  ,,  Author. 

24.  1,  )>  English. 

32.  Distance  for  sympathetic  detonation.     Abbot. 

58.  Collapsing  pressure.     Raiikine. 

60,  82.  Thickness  of  mine  case.     Author. 

62,  68.  Pressure  due  to  current.     Fronde. 

91,  94.  Weight  required  for  sinker.     Author. 

115.  Theory  of  bridge  of  wire  fuze.     Abbot. 

132.  Firing  current,  law  of.     Ohm. 

144,  145.  Conmiand  rciiuired  for  depression  firing.     Author. 

15C.  Liijuid  resistance  and  E.M.F.  of  firing  battery. 

157.  „  ,,  of  other  batteries. 

217.  Silvered  glass  reflectors. 

218,  line  23.  Dispersion  in  terms  of  dimension  of  source  of  light. 


-'V- 

JHIV3RSIT7] 


SUBMARlSE^MINmG. 


CHAPTER  I.— INTRODUCTORY. 

Also  Analysis  of  Important  Experiments,  and  op  Actual  Results 
IN  War. 

Submarine  warfare,  whether  it  be  carried  on  by  means  of  mines  or  tor- 
pedoes, or  shells  fired  through  the  air  from  a  distance,  depends  upon  the 
fact  that  the  explosion  under  water  of  a  charge  of  proper  dimensions 
properly  placed,  will  damage  the  vessel  attacked  so  as  to  place  her 
hors  de  combat,  or  destroy  her.  The  idea  of  attacking  vessels  in  this 
manner  must  have  suggested  itself  to  many  minds  long  before  we  have 
any  records  of  actual  attempts  "being  made,  but  the  difficulties  of 
placing  a  charge  and  of  firing  it  with  certainty  when  so  placed,  were 
enormous  only  a  hundred  years  since  ;  and,  what  now  appears  so  simple 
a  matter,  owing  to  the  progress  in  science,  must  then  have  been  con- 
sidered an  almost  impossible  problem  to  any  but  sanguine  inventors. 

Nevertheless,  more  than  a  century  has  elapsed  since  British  ships 
were  subjected  to  the  attack  of  drifting  torpedoes  in  the  Delaware  River 
during  the  War  of  Independence  ;  and  early  in  the  present  century 
both  Fulton  and  Warner  endeavoured  to  persuade  European  nations 
to  adopt  their  ideas,  but  without  success.  Those  were  hard  times  for 
inventors. 

More  recently  the  Russians  used  small  gunpowder  charged  mines  in 
the  Baltic  during  the  Crimean  War,  but  the  cliemical  fuze  employed 
was  slow  in  its  action,  and  the  results  were  insignificant. 

The  birth  of  the  submarine  mine  and  of  the  torpedo  in  practical 
forms  occurred  in  the  American  War  of  Secession,  and  it  will  be 
interesting  to  record  the  damage  done  by  these  weapons  during  tliat 
war.  The  results  obtained  are  astounding,  for,  at  the  commencement 
of  the  war,  the  Confederates  possessed  no  special  stores,  no  trained 
personnel,  and  but  little  scientific  knowledge  of  the  subject  :  — 

1.  In  December,  18G2,  the  U.S.N,  armoured  vessel  Cairo,  512  tons, 
13  guns,  was  destroyed  by  a  mine  in  the  Yazoo  River. 


2  Submarine  Mining. 

2.  In  February,  1863,  the  U.S.N,  monitor  Montank,  844  tons, 
2  guns,  was  seriously  injured  by  a  mine  in  the  Ogeechee  River. 

3.  In  July,  1863,  the  U.S.N,  armoured  vessel  Baron  de  Kalb,  512 
tons,  13  guns,  was  destroyed  by  a  mine  in  the  Yazoo  River. 

4.  In  August,  1863,  the  U.S.N,  gunboat  Commodore  Barney,  513 
tons,  4  guns,  was  disabled  by  an  electrical  observation  mine  in  the 
James  River.     Charge,  2000  lb.  gunpowder.     Ignition  rather  late. 

5.  In  September,  1863,  the  U.S.A.  transport  John  Farron  was 
seriously  injured  by  a  mine  in  the  James  River. 

6.  In  October,  1863,  the  U.S.N,  armoured  vessel  Ironsides,  3486 
tons,  18  guns,  was  seriously  injured  by  a  spar  torpedo  boat  off  Charles- 
town.     Charge,  60  lb.  gunpowder. 

7.  In  1863  the  Confederate  vessel  Marion  was  destroyed  by  a  mine 
accidentally  when  laying  mines  off  Charlestown. 

8.  In  1863  the  Confederate  vessel  Eltiwan  was  seriously  injured  by 
a  mine  off  Charlestown. 

9.  In  February,  1864,  the  U.S.N,  sloop  of  war  Hoosatonic,  1240 
tons,  13  guns,  was  destroyed  by  a  spar  torpedo  boat  off  Charles- 
town. 

10.  The  torpedo  boat  itself  was  sunk  and  was  never  seen  or  heard  of 
again. 

11.  In  April,  1864,  the  U.S.A.  transport  Maple  Leaf,  508  tons,  was 
destroyed  by  a  mine  in  the  St.  John's  River. 

12.  In  April,  1864,  the  U.S.A.  transport  General  Hunter,  460  tons, 
was  similarly  destroyed. 

13.  In  April,  1864,  the  U.S.N,  flagship  Minnesota,  3307  tons, 
52  guns,  was  damaged  internally  by  a  spar  torpedo  boat  in  Newport 
News.     Charge  53  lb.  gunpowder.     Submerged  6  ft. 

14.  In  April,  1864,  the  U.S.N,  armoured  vessel  Eastport,  800  tons, 
8  guns,  was  sunk  by  a  mine  in  Red  River. 

15.  In  May,  1864,  the  U.S.N,  gunboat  Commodore  Jones,  542  tons, 
6  guns,  was  destroyed  by  an  electrical  observation  mine  in  James 
River.     Charge,  2000  lb.  gunpowder. 

16.  In  May,  1864,  the  U.S.A.  transport  H.  A.  Weed,  200  tons,  was 
destroyed  by  a  mine  in  St.  John's  River. 

17.  In  June,  1864,  the  U.S.A.  transport  Alice  Price,  320  tons,  was 
destroyed  by  a  mine  in  the  St.  John's  River. 

18.  In  Augu.st,  1864,  the  U.S.N,  monitor  Tecumscli,  1034  tons, 
2  guns,  was  destroyed  by  a  mine  in  Mobile  Bay. 

19.  In  October,  1864,  the  Confederate  armoured  vessel  Albemarle, 
2  guns,  was  destroyed  by  a  spar  torpedo  boat  at  Plymouth. 

20.  The  torpedo  boat  sank. 


Actual  Work  ill,  War.  .') 

21.  In  November,  1864,  the  U.S.A.  transport  Greyhound,  900  tons, 
was  destroyed  by  a  coal  mine  in  her  furnace  in  James  River. 

22.  In  December,  1864,  the  U.S.N,  gunboat  Narcissus,  101  tons, 
2  guns,  was  destroyed  by  a  mine  in  Mobile  Bay. 

23.  In  December,  1864,  the  U.S.N,  gunboat  Otsego,  974  tons, 
10  guns,  was  destroyed  by  a  mine  in  the  Roanoke  River. 

24.  In  December,  1864,  the  U.S.N,  tug  Bazley  was  destroyed  by 
a  mine  in  the  Roanoke  River. 

25.  In    January,    1865,   the   U.S.N,    monitor    Patapsco,    844    tons, 

2  guns,  was  destroyed  by  a  mine  off  Charlestown. 

26.  In  February,  1865,  the  U.S.N,  gunboat  Osceola,  974  tons, 
10  guns,  was  crippled  by  a  drifting  torpedo  in  Cape  Fear  River. 

27.  In  1865,  the  Confederate  transport  Sliultz  was  destroyed  l)y  a 
mine  accidentally  in  the  James  River. 

28.  In  March,  1865,  the  U.S.N,  gunboat  Harvest  Moon,  546  tons, 

3  guns,  was  destroyed  by  a  mine  at  Charlestown. 

29.  In  March,  1865,  the  U.S.A.  transport  Thorne,  403  tons,  was 
destroyed  by  a  mine  in  James  River. 

30.  In  March,  1865,  the  U.S.N,  gunboat  Althea,  72  tons,  1  gun, 
was  destroyed  by  a  mine  in  Blakely  River. 

31.  In    March,    1865,   the  U.S.N,    monitor   Milwaukee,    970    tons, 

4  guns,  was  destroyed  by  a  mine  in  Blakely  River. 

32.  In  March,  1865,  the  U.S.N,  monitor  Osage,  523  tons,  2  guns, 
was  destroyed  by  a  drifting  torpedo  in  the  Blakely  River. 

33.  In  April,  1865,  the  U.S.N,  gunboat  Rodolph,  217  tons,  6  guns, 
was  destroyed  by  a  mine  in  Blakely  River. 

34.  In  April,  1865,  the  U.S.N,  gunboat  Ida,  104  tons,  1  gun,  was 
destroyed  by  a  mine  in  Blakely  River. 

35.  In  April,  1865,  the  U.S.N,  gunboat  Sciota,  507  tons,  5  guns, 
was  destroyed  by  a  mine  in  Mobile  Bay. 

36.  In  May,  1865,  the  U.S.A.  transport  R.  B.  Hamilton,  400  tons, 
was  destroyed  by  a  mine  in  Mobile  Bay. 

37.  In  June,  1865,  the  U.S.N,  gunboat  Jonquil,  90  tons,  2  guns, 
was  seriously  injured  by  a  mine  when  raising  frame  torpedoes  in 
Ashley  River. 

When  the  employment  of  mines  and  torpedoes  was  first  conunenced 
by  the  Confederates,  the  Northerners  affected  to  treat  them  with 
indifference.  This  feeling  gradually  wore  away.  The  long  list  of 
vessels  destroyed  proved  the  efficiency  of  submarine  mines  more 
thoroughly  than  any  amount  of  argument. 

A  certain  number  of  people,  especially  those  interested  in  gunnery, 
and  more  recently  those  connected  with  torpedo  boats  or  with  loco- 


4  Submarine  Minhuj. 

motive  torpedoes,  assert  that  the  sphere  of  action  of  a  submarine 
mine  is  very  limited.  But  they  forget  that  the  position  of  a  mine 
being  unknown  to  a  foe,  the  whole  of  any  waters  which  may  be  mined 
must  be  treated  as  if  they  are  known  to  be  mined.  To  insure  this  end, 
mines  should  be  scattered  as  much  as  possible,  and  the  greatest  secrecy 
should  be  maintained  concerning  their  intended  positions,  the  plans  of 
the  mine  fields,  and  the  approximate  position  of  the  mine  fields  being 
known  only  to  a  selected  few,  the  number  of  the  mines  to  be  used  in 
any  harbour  being  kept  secret,  and  misleading  reports  spread  con- 
cerning all  these  matters. 

Soon  after  the  American  War  of  Secession,  European  nations  took 
up  the  subject  in  earnest,  trained  men  in  the  preparation  and  planting 
of  mines,  and  purcliased  the  necessary  stores  and  appliances.  Com- 
mittees were  formed  to  investigate  and  report  upon  the  matter,  after 
making  the  necessary  experiments  ;  but  it  was  not  until  nearly  ten 
years  afterwards  tliat  experiments  with  targets  representing  the  hull 
of  a  modern  warship  were  made  in  Europe  to  discover  with  exactitude 
the  distances  of  destructive  effect  of  various  submarine  explosions. 

England  led  the  way  by  the  long  and  important  series  of  experiments 
against  the  hull  of  H.M.S.  Oberon,  which  was  altered  so  as  to  represent 
the  bottom  of  the  strongest  ironclad  then  afloat,  viz.,  H.M.S.  Hercules, 
which  has  an  outer  skin  about  |  in.  thick  supported  by  frames  forming 
rectangles  about  6  ft.  by  4  ft.,  and  3  ft.  to  the  inner  skin. 

These  experiments  were  described  somewhat  minutely  in  the  Thnes 
by  their  able  reporter  at  Portsmouth,  and  foreign  governments  thus 
obtained  much  useful  information. 

General  Abbot,  of  the  U.S.  Engineers,  lias  for  several  years  been 
engaged  in  the  investigation  of  the  effects  of  submarine  explosions,  and 
his  rejjort  to  Congress  on  the  subject  is  a  classic,  and  contains  tabulated 
information  concerning  the  Oberon  experiments,  but  the  pressures 
recorded  in  the  column  marked  P  (Table  I.),  and  which  are  calculated 
from  General  Abbot's  formula  to  be  examined  in  a  following  chapter, 
may  be  incorrect,  as  the  formula  does  not  give  results  agreeing  with 
some  other  important  and  carefully  conducted  experiments.  If  corrrect, 
"  a  study  of  tlie  figures  in  Table  I.,  and  of  the  injuries  inflicted,  leads  to 
the  conclusion  that  an  instantaneous  mean  pi'essure  of  5500  lb.  per 
square  inch  exceeded  the  resisting  power  of  the  Oberon  ;  and  lionce 
that  such  a  blow  would  cripple  the  Hercules  in  action." 

A  large  number  of  crusher  gauges  were  attached  to  the  sides  of  the 
Oberon,  and  the  results  as  recorded  on  them  liave  never  been  published. 
They  were  unsatisfactory,  probably  due  to  water  getting  into  tlie 
gauges. 


Oheron  "  Experiments. 


s 

1 
%  ll 

1 

Hull  shaken.    Condenser  pipe  split.  No  serious 

damage. 
Hull  shaken.    No  rupture. 
Seriously  shaken.    No  rupture  of  bottom.    Sea 

connections  damaged. 
Outer  plating  buckled.     Rivets  started.     No 

leak.     Condenser,  &c.,  seriously  damaged. 
Outer  plating  much  buckled.     No  leak. 
Small  leaks  started.    No  fatal  rupture.     Outer 

skin  seriously  damaged. 
Fatal  shock.      Ship  sank.     Much  damage  of 

various  kinds. 
Outer  skin  indented  IJin.  (This  experiment  is 

erroneously  recorded  C=75,  and  P  is  there- 
fore too  small. ) 
Fatal  local  shock.  Large  hole  opened  through 

both  skins. 

Ditto                       ditto. 
Ditto                       ditto. 

Ditto  (?') 
Calculated 

by  a  New 

Formula 
now 

proposed 
by  Author. 

4,348 

5,269 
6,581 

7,467 

9,644 
9,644 

15,918 

4,085 
(5,106) 

19,541 

19,430 
19,430 

Pre9BUre(P) 
in  Pounds 
per  sq.  in. 
on  nearest 
point  of 

Hull. 
Abbot's 
Formula. 

1,235 

1,609 
2,196 

2,612 

3.697 
3,697 

5,996 

4,927 

4,155 

19,800 
19,800 

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"  Oheron  "  Experiments.  7 

An  examination  of  experiments  9  and  1 0  on  Table  I.  shows  that  there 
must  be  something  wrong  with  the  pressures  calculated  from  Abbot's 
equation,  as  the  smaller  pressure  could  not  possibly  produce  so  much 
the  greater  effect.  Another  equation  proposed  by  the  autlior,  and  to 
be  examined  in  a  future  chapter,  gives  better  results,  which  are  shown 
in  the  last  column  of  the  Table  now  being  examined.  If  correct,  the 
pressure  required  to  produce  a  fatal  effect  on  an  ironclad  is  much 
nearer  12,000  lb.  on  square  inch  than  5500  lb. 

The  values  for  intensity  of  action  (I)  in  calculations  for  P'  were 
taken  at  25  for  gunpowder  and  100  for  gun-cotton.  In  the  column 
for  P  the  value  87  was  given  to  gun-cotton,  which  is  probably  13 
per  cent,  too  low.  The  values  for  D  are  only  correct  approximately, 
the  precise  form  of  the  Oberon's  hull  being  unknown  to  General  Abbot. 
The  weight  of  the  hull,  &e..  was  1100  tons;  draught,  11  ft.;  length, 
164  ft. ;  beam,  28  ft.  6  in. 

A  condenser  was  fitted  to  the  Oberon,  but  no  boiler  or  machinery. 
A  sheep  and  other  animals  on  board  were  not  injured  by  any  of  the 
experiments.  The  author  remained  on  board  during  one  of  the  ex- 
periments not  recorded  in  the  Table  (100  lb.  gun-cotton  25  ft.  off). 
The  effect  was  a  sharp  jar  on  the  ankle  bones.  Many  other  experiments 
were  made  with  the  Oberon,  but  the  more  important  are  all  recorded 
in  the  Table  now  borrowed  from  General  Abbot. 

About  the  same  date  another  series  of  important  experiments  was 
carried  out  at  Carlskrona  by  a  combined  committee  of  Danish  and 
Swedish  officers.  An  iron  target  representing  the  side  and  bottom  of 
H.M.S.  Hercules  was  inserted  in  a  very  strong  wooden  ship  named  the 
Vorsicticheten. 

These  experiments  were  published  in  Commander  Sleeman's  book  on 
"Torpedoes,  1880,"  and  Abbot's  analysis  now  reproduced  in  Table  II. 
was  drawn  up  from  it.  A  column  is  now  added  for  the  pressure  P^ 
calculated  by  the  author's  formula  to  be  described  hereafter.  An 
examination  of  the  Table  indicates  that  the  results  are  better 
explained  by  column  marked  P'  than  by  column  marked  P. 

If  experiments  numbered  8,  9,  11  be  compared,  the  pressures  under 
P  ai'e  nearly  the  same,  although  the  results  are  so  widely  different.  Thus 
"  no  injui-y  "  is  recorded  against  No.  8  ;  "  plates  indented  "  against 
No.  9  ;  and  "a  hole  through  both  bottoms  "  against  No.  11. 

Some  experiments  were  carried  out  by  the  Austrian  Government  at 
Pola  in  1875,  and  are  recorded  in  Abbot's  report.  Target,  a  pontoon  ; 
draught  of  water,  19  ft.  ;  60  ft.  long,  40  ft.  beam,  with  circular  ends, 
and  fitted  with  a  condenser  and  two  Kingston  valves,  and  with  a 
double  bottom  to  represent  the  Hercules. 


Submarine  Mining. 


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?Sc?SJS;^£S£;SSSg   s^ssss 


Miscellaneous  Eocpenments.  9 

Experiment  1. — 0  =  617  lb.  dynamite,  D  =  53  ft.,  D  liorizontal  = 
G2  ft.  from  keel,  submersion  40J  ft.  ;  depth  of  water  GO.',  ft.  at  charge 
and  62  ft.  at  target.  Effects :  outer  skin  slightly  indented,  a  few 
rivets  started,  several  screws  of  valves  loosened. 

Experiment  2. — 0  =  585  lb.  dynamite,  D  =  48  ft.,  D  horizontal  = 
60  ft.  from  keel,  submersion  36  ft.  ;  depth  of  water,  78  ft.  at  charge, 
74  ft.  at  target.  Effects  :  some  rivets  loosened,  a  few  angle  irons 
sheared,  outer  skin  slightly  indented,  no  damage  to  condenser  or 
valves.  In  each  experiment  the  charge  was  placed  opposite  the  centre 
of  the  pontoon. 

On  Table  III.  is  given  Abbot's  analysis  of  miscellaneous  experiments, 
<fec.,  a  column  being  added,  as  before,  showing  the  pressures  calculated 
by  the  author's  formula  to  be  described  hereafter. 

General  Abbot's  remarks  on  this  Table  are  as  follows  : 

1.  "  Except  in  the  uncertain  and  anomalous  gunpowder  trials  upon 
the  Wagram  and  the  Requin  (the  former  vessel  not  described,  and  the 
latter  a  very  small  craft)  in  every  instance  where  the  computed  mean 
pressure  exceeded  our  adopted  standard  of  6500  lb.  per  square  inch  " 
(as  calculated  by  General  Abbot's  equations)  "  the  vessel  was  destroyed." 

2.  "  The  injuries  to  the  Terpsichore,  and  to  the  Conklin  and  Olive 
Branch,  show  that  an  ordinary  wooden  hull  will  not  always  endure  a 
computed  mean  pressure  of  1500  lb.  per  square  inch." 

By  the  author's  formula  these  pressures  appear  to  be  much  greater 
than  1500  lb.,  viz.,  10,000  lb.  and  19,000  lb. 

3.  "  The  injuries  inflicted  upon  the  Ironsides  and  Minnesota  indicate 
that  3000  lb.  per  square  inch  exceeds  the  limit  of  safety  even  for  a 
strong  wooden  hull.  The  blow  received  by  the  latter  is  especially 
interesting  as  fixing  her  extreme  endurance." 

Experiment  No.  9  on  the  Oberon  series  proves  conclusively  that 
the  distances  recorded  against  the  Ironsides  and  Minnesota  must  be 
erroneous. 

4.  "  The  trials  upon  the  Austiian  pontoon  confirm  the  conclusion 
that  the  recoil  of  a  target  reduces  the  eflect  upon  it " 

5.  "  The  discrepancies  exhibited  by  some  of  the  gunpowder  experi- 
ments, and  the  remarkable  uniformity  shown  by  those  with  gun- 
cotton  and  dynamite,  confirm  the  conclusion  reached  when  testing  these 
explosives  in  rings"  fitted  with  crusher  gauges,  to  be  described  in 
another  chapter.  The  conclusion  referred  to  was  that  explosive  mixtures 
appear  to  act  with  a  decided  maximum  intensity  in  some  one  direction 
at  each  explosion.  In  other  words,  that  there  is  a  marked  burst  of 
gas  from  such  an  explosion,  but  that  it  is  as  likely  to  occur  in  one 
direction  as  another.      With  explosive  compounds  no  such  erratic  action 


10  Submarine  Mining. 

was  observed.     This  is  one  of  several  reasons  for  preferring  the  com- 
pounds to  the  mixtures  for  submarine  mining. 

The  following  additional  information  concerning  some  of  the  entries 
on  Table  III.  is  taken  from  General  Abbot's  report: 

1.  The  Dorothea,  a  strong  200-ton  brig,  was  blown  up  in  England 
by  Robert  Fulton  in  1805. 

2.  H.M.S.  Terpsichore,  sloop-of-war,  10  ft.  draught,  was  blown 
up  in  1865  in  England.  The  charge  was  2  ft.  clear  of  the  ship, 
horizontally. 

3.  This  target  was  an  iron  case  20  ft.  long  by  10  ft.  high  by  8  ft. 
deep  or  thick.  It  had  six  compartments,  being  divided  by  one  ^-in. 
longitudinal  bulkhead  and  two  |-in.  cross  bulkheads.  The  front  and 
rear  faces  were  W  in.  thick. 

Large  pieces  of  iron  were  hurled  nearly  200  ft.  in  the  air  and  to  a 
distance  of  about  100  yards. 

Experiments  4  to  24  on  the  Table  were  carried  out  in  France,  and 
but  little  is  known  about  them.  The  Prudence  had  some  kind  of 
plating  on  her  side  presented  to  the  explosions.  The  dimensions  of 
the  vessels  were  as  follows  : 


Table  IV 

ft.      ft. 

ft. 

Recjuin 

95  by  16  by 

4.5  draught 

Express 

108  „   20  „ 

6.6       „ 

Mane 

115  „   21  „ 

7.2      „ 

Cormoran       .  . 

131  „   25  „ 

7.7      „ 

Eldorado       ... 

213  „   39  „ 

10.8      „ 

Prudence 

117  „    49  „ 

14.3      „ 

It  is  impossible  to  .say  mucli  about  these  experiments,  because  the 
relative  strengths  of  the  hulls  and  the  weights  on  board  and  the  method 
of  mooring  adopted  are  all  unknown. 

As  a  result  of  the  series,  the  French  commission  recommended  the 
following  charges  for  ground  mines  : 


Ta 

BLE  V. 

Depth  of  Water. 

Gun-cotton, 

Gunpowder. 

ft. 

lb. 

lb. 

26  to  30 

550 

L"20() 

50 

660 

3300 

60 

880 

4400 

67 

1100 

73 

1320 

80 

1540 

The  cliarges  of  gun-cotton  appear  to  vary  nearly  as  tlie  deptlis.    Tims, 
30  :  80  ::  550  :  1467. 
At  the  smallest  submersion  the  gunpowder  cliarge  is  four  times  the  gun- 
cotton  cliarge,  and  the  ratio  of  charge  to  deptli  is  also  retained.     Thus, 
30  :  60  ::  2200  :  4400. 


Formuke.  1 1 

The  charges  are  certainly  larger  than  necessary,  and  the  practice  of 
employing  ground  mines  in  very  deep  water  is  not  to  be  recommended. 

The  Austrian  experiments  Nos.  26  and  27,  on  Table  III.,  have 
already  been  described.  No.  25  was  carried  out  in  order  to  test  the 
effect  of  a  large  charge  on  a  wooden  vessel.  It  would,  in  all  proba- 
bility, have  been  equally  effective  at  double  the  distance. 

The  German  gunboat,  destroyed  in  experiment  No.  28,  Table  III., 
was  strengthened  internally.  The  charge  was  placed  directly  under 
the  vessel's  keel,  and  the  result  proves  how  tremendously  the  effect  on 
a  vessel  is  increased  when  the  line  of  least  resistance  from  a  gunpowder 
charge  lies  through  the  hull.  The  force  of  the  explosion  is  directed, 
and  the  damage  is  much  greater  than  the  calculated  pressures  would 
indicate.  Experiments  numbered  29,  30,  and  31  on  Table  III.  are  of 
no  value ;  No.  29  because  fhe  result  ought  to  have  been  a  foregone 
conclusion,  and  Nos.  30  and  31  because  the  distances  of  the  charges 
from  the  hulls  are  evidently  erroneous,  which  can  be  proved  by  com- 
paring with  No.  9  (on  Table  I.)  of  the  Oberon  experiments. 

The  last  two  experiments  on  Table  III.  are  chiefly  interesting  because 
the  pressures  as  calculated  by  Abbot's  equations  are  so  low,  although 
the  vessels  were  blown  to  atoms.  In  the  case  of  the  Olive  Branch, 
50  lb.  of  gunpowder  at  3  ft.  gives  a  calculated  pressure  of  only  1421  lb. 
on  the  square  inch,  according  to  General  Abbot ;  but  in  No.  9  experi- 
ment on  Oberon  Table,  66  lb.  of  gunpowder  at  3  ft.  he  calculated  to 
give  a  pressure  of  4155  lb.  on  the  square  inch.  The  pressures  calcu- 
lated by  the  formula  proposed  by  the  writer  of  this  paper  are  19,541 
for  the  one  and  19,125  for  the  other,  which  appear  much  more  reason- 
able, and  would  account  for  the  great  destruction  recorded. 

The  formula  are  as  follows,  and  they  will  be  carefully  examined  in 
Chapter  III. 

General  Abbot's  formula, 

(1^  g.023  C'-S^X  - 
]  ^  for  explosive  mixtures. 

P=  f^^9A"-+^S^\i  for  explosive  compounds. 
^    (D  +  0.01)=     f 
Lieut. -Colonel  Bucknill's  formula, 

P  =  ^^  /'  1  +  '^W  1  +  ^  X  --A  for  all  explosives 
D     V        li'J  \        90     100^  ^ 

and 

P=  (  I  +~'^\  ditto  in  horizontal  plane  only. 

D     V        D-V 

In  these  equations, 

P=pressure  per  square  inch  on  nearest  point  of  target  in  pounds. 

C  =  charge  of  explosive  in  pounds. 

D=: distance  from  centre  of  C  to  target  in  feet. 


12  Submarine  Mining. 

Also  : 

M  =  a  value  found  by  experiment  with  the  different  explosive  mixtures. 

E  =  ditto,  with  the  different  explosive  compounds. 

Irrelative  intensity  of  action  of  the  explosive,  dynamite  being  100. 

a  =  angle  from  nadir  of  direction  of  the  target  from  centre  of  charge,  in  degrees. 

^  =  angle  from  horizontal  plane  of  ditto,  plus  if  above,  minus  if  below. 

e  =  a  ^alue  (in  the  nature  of  a  percentage)  dependent  on  the  explosive. 

S  =  submersion  of  charge  in  feet. 

R  =  radius  in  feet  of  sphere  of  explosive  mixture  ignited  by  one  fuze. 
The  value  of  M  adopted  after  experi-  f  =  ,lf,  ^^"^  mortar  powder, 
ments  by  General  Abbot  ...         ...  |  ='-"^        "'"^''""' 

The  value  of  E  which  depends  on  [ 
relative  intensity  of  action  of  the  ex--^ 
plosive        

The  value  of  I  adopted  by  the  author  | 
differs  somewhat I 

The  value  of  e  for  vertical  action  in  J 
the  author's  formula         1 

General  Abbot  assumes  that  an  instantaneous  mean  pressure  of 
6500  lb.  on  the  square  inch  will  give  a  fatal  blow  to  a  modern  iron- 
clad. 

1  lie  author  assumes  that  a  pressure  of  1 2,000  lb.  is  required. 

It  -will  now  be  convenient  to  examine  the  apparatus  for  measuring 
these  pressures,  which  have  been  used  in  various  countries. 


=  1554  , 

,    musket      ,, 

=  3331  , 

,    sporting    ,, 

=    186  , 

dynamite    No.    1       (1    being 

100). 

=    135  , 

gun  cotton.    (I  being  taken  = 
8i ). 

=   lOQ  , 

dynamite  No.  1. 

=    100  , 

gun-cotton. 

=     25  , 

gunpowder. 

=     20  , 

,    dynamite. 

=     20  , 

,   gun-cotton. 

=     35  , 

gunpowder. 

13 


CHAPTER  II. 

On  the  Apparatus  Employed  for  Measuring  the  Effects  of 
Submarine  Explosions. 

The  records  of  the  early  experiments  made  in  order  to  discover  the 
laws  that  govern  subaqueous  explosions  are  neither  interesting  nor  in- 
structive, except  to  prove  how  little  was  known  of  the  subject  twenty 
years  ago.  After  trying  mechanical  contrivances  of  various  kinds,  the 
happy  thought  of  examining  the  surface  of  a  mud  flat  after  the  explo- 
sion of  a  charge  upon  it,  suggested  itself  to  a  member  of  one  of  the 
English  committees,  and  a  series  of  experiments  giving  for  the  hrst  time 
good  and  trustworthy  results  were  accordingly  instituted.  A  site  was 
chosen  where  there  was  a  considerable  rise  and  fall  of  tide,  so  that  the 
charge  could  be  placed  on  the  mud  at  low  tide  and  be  fired  with  a  good 
submergence  at  high  water. 

A  series  of  experiments  were  also  made  in  England,  in  which  the 
instantaneous  photographs  of  the  columns  of  water  thrown  up  by 
various  charges  were  examined,  and  some  useful  formulae  deduced  there- 
from by  Captain  W.  de  W.  Abney,  R.E.,  F.R.S.,  &c.  These  formulae 
have  only  been  published  confidentially,  so  that  they  cannot  be  repro- 
duced here. 

The  Americans  also  made  some  experiments  by  means  of  photo- 
graphy, but  discarded  them  as  being  of  insufficient  exactitude. 

In  1851  General  Rodman,  of  the  United  States  army,  invented  the 
pressure  gauge  known  by  his  name,  and  used  in  ordnance  experiments. 
It  consisted  of  a  small  cylinder  containing  a  piston  which  drove  a  V- 
shaped  indenting  tool  upon  a  disc  of  pure  copper. 

In  1865  Major  King,  of  the  United  States  Engineers,  applied  it  for 
measuring  the  effects  of  subaqueous  explosions. 

In  1869  Captain  \V.  H.  Noble,  R.A.,  invented  his  crusher  gauge  for 
measuring  the  gas  pressures  produced  inside  the  bores  of  guns  when 
they  are  fired.  It  consisted  of  a  piston  and  cylinder,  the  movement  of 
the  former  crushing  longitudinally  a  small  solid  cylinder  or  pellet  of 
copper,  the  amount  of  compression  giving  a  record  of  the  pressure  to 
which  the  crusher  gauge  had  been  subjected,  the  amount  of  pellet  com- 


14 


Sith: 


Mini 


imj. 


pression  pi'oduced  by  different  statical  pressures  having  previously  been 
ascertained  experimentally. 

Soon  afterwards  a  modification  of  this  crusher  gauge  was  introduced 
into  America  for  employment  in  the  submarine  experiments.  Lead 
pellets  were  used  instead  of  copper ;  the  inside  of  the  cylinder  was 
roughened  by  a  number  of  horizontal  corrugations,  and  small  spring 
catches  engaging  in  these  corrugations  were  attached  to  the  piston  so 
that  it  should  not  hammer  the  pellet  by  a  series  of  blows,  experience 
having  shown  that  this  occurred  when  unroughened  gauges  were  sub- 
jected to  the  effects  of  submarine  explosions.  Water  was  excluded  by 
a  rubber  cap  over  the  end  of  the  cylinder  and  secured  to  it  by  a  band 
engaging  at  the  groove  A  (see  Figs.  1  to  4).  The  cylinder  was  screwed 
Fig  7 


Tlci.Z 


f?nri?> 


Tig  4 

■75 

fi 

Do 


into  a  socket  with  two  ears  to  engage  an  iron  ring  (shown  in  section 
on  the  drawing),  and  was  fixed  thereto  by  a  wedge  and  cotter. 

Pellets  of  different  diameters  were  used  in  order  to  obtain  the  desired 
sensitivity.  Also  rings  of  different  diameters,  .3  ft.,  4  ft.,  5  ft.,  6  ft.,  8  ft. 
in  diameter.  The  gauges  could  also  be  attached  to  the  iron  bars  of  a  large 
framework  crate  which  was  made  for  the  American  experiments.  This 
crate  was  50  ft.  long,  the  effects  as  recorded  on  crusher  gauges  attached 
thereto  could  therefore  be  ol)tained  up  to  a  distance  of  about  25  ft.  from 
a  charge  exploded  in  the  centre. 

In  1873  the  War  Office  Torpedo  Committee  (England)  caused  similar 
apparatus  to  be  manufactured,  but  no  provision  was  made  against  the 
hammering  action  already  alluded  to,  and   water  was  kept  out  simply 


Crusher  Gauges. 


by  the  perfection  of  the  fit  between  the  piston  and  the  cyliuder  in  the 
crusher  gauges.  The  results  of  the  crusher  gauge  experiments  in 
England  were,  on  the  whole,  unsatisfactory,  and  this  may  have  been  due 
to  the  omission  of  the  spring  catches  so  carefully  fitted  to  the  American 
gauges.  Moreover,  when  the  English  crusher  gauges  were  submerged  a 
long  time  before  an  experiment  was  carried  out,  inaccuracy  may  have 
been  caused  by  the  entrance  of  water  into  the  gauge  cylinders. 

The  pellets  used  in  England  were  0.5  in.  long  and  0.326  in.  in  dia- 
meter =tW  square  inch  sectional  area.  Both  lead,  hardened  with 
antimony,  and  copper  were  employed.  The  latter  was  found  to  give 
the  most  reliable  results. 


Bq    G 


.ar® 


The  piston  area  struck  by  the  explosion  varied  ;  in  some  gauges  it 
was  i  square  inch,  in  others  it  was  as  much  as  |  square  inch. 

Fig.  5  shows  the  general  arrangement  of  one  of  the  5-ft.  ring  gauges. 

a  is  the  section  of  ring;  h  is  the  socket;  c  lead  or  copper  pellet;  d  steel 
footplate  ;  e  rubber  washer  ;  /rubber  ring ;  g  steel  piston  ;  h  screw  plug 
and  guide  for  the  piston  ;  k  wooden  wedge.  A  small  bent  steel  spring 
engages  under  h  and  over  the  enlarged  portion  of  the  piston,  keeping 
the  latter  firmly  against  the  pellet. 

Another  form  of  English  crusher  gauge  is  shown  on  Fig.  6,  and  is 
screwed  into  the  bottom  of  a  solid  18-pounder  shot  provided  with  an 
eye-bolt  at  the  top  by  which  it  is  suspended  from  a  fioat.     Or  the  gauge 


16 


Submarine  Minviig. 


may  be  one  of  several  screwed  into  tlie  side  of  a  13-in.  shell,  or  into  the 
side  of  a  cast-iron  sinker,  or  any  other  substantial  metal  body.  The 
pellet  is  centered  by  a  rubber  ring  inside  a  piston  which  is  kept  in  place 
by  two  screws  as  shown.  The  pellet  is  seated  on  a  projection  forming 
part  of  the  steel  cylinder.  Three  holes  are  provided  at  the  bottom  of 
the  cylinder  so  that  the  piston  can  be  forced  out  after  the  experiment 


by  means  of  a  three-pronged  fork.  Tlie  bottom  is  made  water-tigiit  Ijy 
a  sheet  of  lead  or  india  rubber.  Other  modilitations  were  used,  and  the 
above  are  typical  of  them  all. 

The  results  of  the  English  experiments  have  not  been  published,  but 
it  may  be  stated  that  the  best  as  well  as  the  highest  compressions  for 
given  distances  were  obtained   in  the   gauges  lixed  to  shot   and   shell 


Crusher  Oaityes.  J  7 

simply  suspended  in  the  water  and  almost  free  to  move  with  it.  This 
is  curiously  in  contradiction  with  the  published  results  of  the  American 
experiments. 

Other  modifications  of  Captain  Noble's  gauges  were  soon  introduced 
for  the  experiments  with  submarine  explosions  made  in  foreign  countries. 
Thus  in  France  it  is  understood  that  a  gauge  made  somewhat  as  shown 
on  Fig.  7  was  used  in  a  number  of  experiments,  the  details  of  which, 
however,  have  been  carefully  kept  secret.  The  gauge  consisted  of  a  hat- 
shaped  metal  body  a,  b,  c,  d,  e,  with  an  eye-bolty!  Rubber  washers  g  (/, 
a  steel  piston  k,  a  rubber  diaphragm  I,  a  ring  washer  m,  and  clamps  n  n. 
The  lead  pellet  h  of  dimensions  figured  was  much  larger  than  those  used 
in  England. 

It  was  not  very  difficult  to  improve  upon  this  gauge,  and  Captain 
Eckermann,  of  the  Swedish  Engineers,  did  this  by  adopting  the  form  of 
piston  used  in  one  of  the  English  gauges  already  described,  using  an 
india-rubber  washer  instead  of  a  diaphragm,  decreasing  the  diameter  of 
the  ring  washer,  and  lipping  it  so  as  to  engage  the  rubber  between  it 
and  the  top  of  the  piston,  and  using  a  screw  cap  in  place  of  the  clamps 
and  steel  centering  pins  instead  of  the  two  rubber  rings  round  the  pellet. 
He  thus  produced  the  gauge  shown  in  Fig.  8  ;  three  gauges  were  placed 
back  to  back  at  120  deg.,  the  whole  forming  the  crusher  gauge  now 
known  as  "  Eckermann's."  It  costs  4^.,  and  1000  lead  pellets  with 
necessary  tools  cost  161. — total  for  six  and  1000  pellets,  401.  The 
great  defect  in  this  crusher  gauge  is  the  same  as  that  in  all  the  European 
forms  of  Noble's  gauge,  viz.,  that  no  provision  is  made  to  prevent  the 
piston  jumping  in  and  out,  and  hammering  the  pellet  by  a  series  of  blows 
which  are  not  always  given  in  the  direction  required.  Pellets  are  some- 
times extracted  from  these  gauges,  as  shown  in  sketch,  Fig.  9,  indicating 
that  after  the  first  blow  the  piston  has  jumped  back  and  released  the 
pellet  from  the  centering  pins  ;  the  pellet  has  then  toppled  and  received 
a  second  blow  while  in  a  tilted  position,  and  then  several  smaller  blows. 
The  centering  pins  are  evidently  inferior  to  the  rubber  rings  used  in  the 
English  and  French  gauges  for  the  same  purpose,  and  the  necessity  of 
some  arrangement,  as  in  the  American  gauges,  for  preventing  the  piston 
from  moving  backwards  is  very  apparent. 

The  records  from  these  gauges,  when  applied  to  submarine  explosions, 
are  distinctly  inferior  to  those  obtained  in  tlie  English  experiments  with 
small  pellets  of  copper  or  lead.  Thus,  taking  haphazard  one  of  the 
English  experiments,  a  13-in.  shell  fitted  with  four  copper  pellet  gauges 
gave  .019,  .015,  .021,  .018,  and  four  lead  pellet  gauges  in  the  same  shell 
gave  .166,  .174,  .166,  .170.  In  some  records  with  Eckermann's  gauge 
we  find  in  one  triple  gauge  .05.'),  .065,  .025,  differing  more  than  100  per 
c 


18 


Submarine  Mining. 


cent.  In  another  experiment  a  triple  gauge  gave  .095,  .103,  .079.  In 
anotlier,  .105,  .105,  .087.     In  another,  .091,  .130,  .115. 

Very  few  experiments  with  the  piston  and  cylinder  type  of  crusher 
gauge  have  been  made  in  England  since  the  conclusion  of  the  ex- 
periments against  the  Oberon.  But  a  tubular  form  of  dynamometer 
has  been  adopted  into  the  service  which  in  its  earliest  form,  sliown  on 
sketch  (see  Figs.  10,  11,  and  12),  was  invented  and  proposed  by  the 
author  in  February,  1876.  It  acts  on  the  collapsible  principle,  and 
the  work  performed  upon  it  is  measured  by  the  difference  in  the 
amount  of  its  cubical  content  before  and  after  an  experiment. 

The  results  obtained  with  the  first  form  of  tliis  dynamometer  were 
encouraging ;  and  it  has  gradually  been  improved  by  the  inventor  until 
it  has  now  become  trustworthy.  In  the  latest  (1886)  patterns  the 
tubes  are  made  of  commercially  pure  lead  obtained  by  the  desilverising 
process.  The  tubing  is  run  from  a  special  die  of  elliptical  section 
(Fig.  13)  l|-in.  major  axis  and  l|-in.  minor  axis,  with  a  circular  core 


Ivq.W. 


•%J^ 


\\  in.  in  diameter.  The  tubing  is  cut  into  short  lengths,  straightened 
and  trimmed  to  exactly  6  in.  in  length  with  a  smooth,  flat,  and  square 
surface  at  each  end.  They  are  then  packed  in  perforated  wooden  slabs 
in  boxes  so  that  they  do  not  touch,  and  cannot  damage  each  other  or  be 
damaged  in  transit ;  fifty  tubes  are  placed  in  one  box. 

When  used  to  measure  the  effects  of  explosions,  three  tubes  are 
placed  in  a  cage  formed  as  follows.  The  top  consists  of  a  circular  plate 
of  |-in.  iron  4i  in.  in  diameter  with  a  central  }-g-in.  hole.  To  this  is 
secured  at  one  end  an  iron  cage  8  B.W.Gr.  thick,  7  in.  long,  and  per- 
forated with  seven  I'ows  of  |-in.  holes,  seven  holes  per  row.  Tlie 
bottom  plate,  loose,  is  similar  to,  but  |  in.  smaller  in  diameter  tlian, 
the  top  plate.     (See  Figs.  14  and  15.) 

For  each  plate  is  provided  an  india-rubber  disc  |  in.  thick,  4|  in.  in 
diameter,  with  a  central  |-in.  hole.  A  f-in.  eye-bolt  with  a  nut  at  the 
lower  end  secures  the  whole  together,  three  tubes  being  previously 
inserted  between  and  square  to  the  india-rubber  discs.     Care  should  be 


Ui/namometers. 


taken  not  to  screw  up  one  cage  of  tubes  more  tightly  than  another. 
Tliese  cages  are  usually  suspended  by  a  small  wire  rope,  with  eye  and 
shackle,  from  floating  spars,  the  distance  from  the  charge  being 
measured  on  the  spar,  and  the  required  submersion  on  the  wire  rope. 
The  cages  cost  51.  per  dozen,  and  the  tubes  cost  19^.  per  1000,  but  the 
old  lead  after  the  experiments  can  be  sold  for  about  12^.  per  1000. 
Hence  the  cost  of  the  tubes  does  not  exceed  71.  per  1000.  The 
pellets  for  Eckermann's  gauges  are  much  lighter.      Comparing  cost : 


12  of  the  above  cages  and  1000  tubes     ... 
12  Eckermann's  holders  and  1000  pellets 


12/. 
54/. 


JAo/d/nj  boiti 


The  accuracy  of  the  tubular  dynamometers  has  been  thoroughly 
established,  the  compressions  of  the  three  tubes  in  a  cage  subjected  to 
an  explosion  being  almost  identical.  Thus  the  greatest  difference  of 
any  one  tube  from  the  mean  of  three  in  the  cage  was  found  to  be  in  sLx 
cages,  and  in  one  of  the  large  charge  experiments  as  follows  :  Greatest 
difference  from  mean,  cage  (a),  1.6  per  cent.;  (6),  3.2  per  cent.;  (c), 
0.2  per  cent.;  (d),  2.4  per  cent.;  (e),  4  per  cent.;  (/),  2  per  cent. 

The  best  way  to  measure  the  tubes  is  to  get  some  carefully  washed 


20  Submarine  Mininy. 

sand  not  too  fine  (silver  sand  is  too  line),  and  dry  it  and  let  it  cool. 
Place  a  tube  on  a  small  piece  of  cardboard,  quarter  fill  with  sand  and 
tap  the  tube,  half  fill  and  repeat  tapping,  three-quarter  fill  ditto,  fill 
and  tap,  and  fill  and  tap  until  no  more  sand  can  go  in.  Then  strike 
top  surface  level,  and  weigh  the  sand  carefully  =  W.  After  the  ex- 
periment repeat  =  W.  Then  W  -  W  =  compression.  And  a;  :  100  : ; 
W  -  W  :  W.  X  is  the  percentage  of  capacity  compressed,  and  forms 
the  method  of  comparison  adopted ;  it  is  independent  of  the  specific 
gravity  of  the  material  used  for  measuring  the  compression. 

In  order,  if  possible,  to  dovetail  the  records  from  these  dynamometers 
with  those  from  the  piston  and  cylinder  type  of  crusher  gauges,  ex- 
periments have  been  carried  out  to  find  the  compressions  produced 
when  the  tubes  were  placed  in  a  closed  cylinder  filled  with  water  and 
subjected  to  the  hydro-dynamic  effect  produced  by  a  weight  falling  upon 
a  small  movable  plunger.     A  very  strong  metal  cylinder  5  in.  in  dia- 


meter and  about  1  ft.  long  ^internal  dimension  was  used,  and  the 
cylinder  cover  was  fitted  with  a  movable  plunging  rod  having  a 
sectional  area  of  1  square  inch.     (See  Fig.  16.) 

The  fall  of  10  lb.  through  10  ft.  on  this  plunger  produced  the 
following  curious  records  on  the  tubes  when  three  of  them  in  one  cage 
were  subjected  to  the  blows  : 


Trial  1.   W-W 


Mean. 
217 


:479  61  32 

2.         „  39  228  485 

These  unexpected  results  proved  how  very  different  is  the  blow  given 
by  an  explosion  to  that  given  in  the  experiment.  In  the  one  the  three 
tubes  are  compressed  nearly  equally,  in  the  other  the  compression  of 
the  weak  tubes  saves  the  others. 

It  occurred  to  the  author  that  the  trial  should  be  made  with  one  tube 
only  in  the  cylinder,  and  a  special  cage  was  made  (for  a  single  tube) 
consisting  of  two  plates  and  rubber  discs  braced  together  by  two  bolts, 


Dynamometers. 


21 


one  on  each  side  of  the  tube  to  be  tested  (see  Fig.  17).  A  blow  of 
100  footpounds  on  the  plunger,  caused  by  the  fall  of  a  20-lb.  weight, 
now  gave  in  three  separate  trials  on  three  tubes  taken  singly  the 
following  values:  W  -  W  =  230,  314,  288,  mean  277;  or,  14.66  per 
cent,  of  W  =  1900.  Continuing  the  results  of  trials  with  20-lb.  falling 
weight  : 

Table  VI. 


ft. 
Falling  2   -- 


ft. -lb. 
40  gave  a;,  or  per  cent,  of  W 


100 


Mean 

Value. 

2.76 


2.37  -  = 
}.0  J 

.47  U 
.21 J 


7    =140 


2.9 

2.: 

3.1 

7.37 

7.' 

7.68^ 

9.42-, 
11. 
11. 
12.21-, 

).62 

leJ 

.21.26. 

{  20.21 

120.42-' 

(-23.0  -> 

]  25.42^24.33 

'-24. 58  J 


(-30.26-, 
{  30.68 
V  32. 37  J 


.12.i 
{  16.f 
U5.I 


10.7 


14.66 


:  20.63 


=  31.10 


10    =200 


r40.0  -, 
{  34.68 
138.37-' 
(-40.0  -> 
{  43.05 
U3.68-' 


The  compressibility  of  water  was  clearly  shown  by  the  monkey  being 
thrown  back  to  a  height  of  from  15  to  20  per  ceirt.  of  the  fall.  It  was 
then  caught  and  not  allowed  to  fall  a  second  time  on  the  plunger.  The 
above  values  were  slightly  increased  by  halving  the  quantity  of  water 
in  the  cylinder,  by  the  introduction  of  a  large  lump  of  iron  about  5  in. 
in  diameter  and  6  in.  long.  The  result  was  evidently  due  to  less 
energy  being  absorbed  in  compressing  the  water,  there  being  less  water 
to  press.  It  would  be  very  interesting  to  find  by  experiments  whether 
the  above  values  can  be  equated  with  hydrostatic  pressures  applied  to  a 
similar  or  to  the  same  cylinder,  the  hole  for  the  plunger  being  closed  by 
a  screw  plug.  The  values  just  given  when  plotted  graphically  on  a 
diagram  where  the  abscissa  are  foot-pounds  applied,  and  the  ordinates 
the  values  for  x  obtained,  produce  a  line  almost  straight. 

The  lead  pellets  for  the  Eckermann's  crusher  gauges  have  been  sub- 
jected to  similar  blows  given  by  a  weight  of  22  lb.  1  oz.  falling  through 


22 


Subr)iarine  Mining. 


various  heights.     Each  pellet  is  55  mm.  long  and  20  mm.  in  diameter, 
or  0.4856  square  inch  sectional  area. 

Table  VII. — Compressions— Large  Lead  Pellets. 


Foot- 

Compression 
in  Inches. 

Foot- 

Compression 

Foot- 

Compression 
in  Inches. 

Foot- 

pounds. 

pounds. 

in  Inches. 

pounds. 

pounds. 

in  Inches. 

20 

.13 

120 

.51 

220 

.705 

320 

.84 

40 

.23 

140 

.56 

240 

,73 

340 

.87 

60 

.31 

160 

.60 

260 

.755 

360 

.89 

80 

..38 

180 

.64 

280 

.78 

380 

.93 

100 

.45 

200 

.68 

300 

.81 

400 

.96 

The  pellets  used  in  the  English  crusher  gauges  were  also  subjected  to 
similar  blows  from  a  falling  weight  of  25  lb.  In  the  following  Table 
the  blow  in  foot-pounds  and  the  compressions  of  a  copper  pellet  ^  in 
long  and  yV  square  inch  section  are  given,  also  a  column  of  means,  and 
the  same  corrected  by  a  curve.  Also  in  the  last  column  are  recorded 
the  actual  statical  pressures  which  by  other  experiments  were  found  to 
produce  the  same  compressions. 

Table  VIII. 


Twenty-five 
Pounds 

Foot- 
pounds. 

Compression  in  Inches. 

Pressure  Pro- 
ducing the  same 
Compression. 

Fall  in 
Inches. 

First. 

Second. 

Third. 

Mean. 

Corrected. 

3 

.036 

.038 

.043 

.039 

.039 

lb. 
2365 

6 

12.5 

.058 

.059 

.063 

.060 

.060 

3050 

9 

.066 

.070 

.079 

.072 

.078 

3615 

12 

25 

.090 

.092 

.094 

.092 

.094 

4095 

15 

.104 

.105 

.105 

.105 

.108 

4515 

18 

37.5 

.116 

.116 

.117 

.116 

.121 

4906 

21 

.125 

.128 

.136 

.130 

.133 

5305 

24 

50 

.143 

.145 

.148          .146 

.144 

5645 

27 

.148 

.151 

.152 

.151 

.154 

5965 

30 

62.5 

.160 

.162 

.166 

.163 

.163 

6280 

33 

.167 

.168 

.169 

.168 

.171 

6535 

36 

75 

.177 

.178 

.179 

.178 

.179 

6795 

39 

.184 

.188 

.189 

.187 

.187 

7070 

42 

87.5 

.190 

.191 

.191 

.191 

.194 

7295 

45 

.200 

.201 

.203 

.202 

.201 

7540 

48 

100 

.204 

.207 

.207 

.206 

.208 

7820 

51 

.208 

.211 

.214 

.211 

.215 

8100 

64 

112.5 

.218 

.221 

.223 

.221 

.222 

8380 

57 

.223 

.226 

.233 

.228 

.228 

8620 

60 

125 

.231 

.232 

.237 

.234 

.234 

8860 

The  numerous  crusher  gauge  experiments  made  by  tlie  War  Depart- 
ment have  never  been  published,  nor  is  the  author  permitted  to  do  so. 
Many  of  them  were  conflicting  and  diflicult  to  explain,  many  on  tlie 
other  hand  were  interesting  and  suggt'stivo. 


23 


CHAPTER   III. 

Theoretic  and  Empiric  Formula  for  Submarine  Explosions. 

Early  in  1874  the  author  pointed  out  that  the  results  of  certain 
crusher  gauge  experiments  in  England  appeared  to  indicate  tliat  the 
effects  of  submarine  explosions,  as  shown  on  the  gauges,  varied 
inversely  as  the  cube  of  the  distance  between  the  centre  of  the  charge 
and  the  surface  of  the  target.  Lieutenant  (now  Major)  English,  R.E., 
then  examined  this  theory,  and  wrote  the  following  very  interesting  and 
important  remarks  thereon,  dated  March  23,  1874  : 

"It  appears  that  a  permanent  compression  of  0.234  in.  is  produced 
by  the  blow  given  by  a  weight  of  25  lb.  falling  through  60  in.  on  a 
copper  cylinder  0.5  in.  long  and  0.083  of  a  square  inch  in  area.  Also 
that  an  equal  compression  is  produced  by  a  steady  pressure  of  3.95  tons 
upon  a  similar  cylinder. 

"  Assuming  that  the  maximum  pressure  produced  during  the  impact 
of  a  falling  weight  varies  with  the  square  root  of  the  height  through 
which  the  weight  falls,*  and  that,  as  above,  the  maximum  pressure 
produced  by  a  weight  of  25  lb.  falling  through  60  in.  on  to  a  copper 
cylinder  of  the  dimensions  given  is  3.95  tons,  the  results  given  in  the 
following  Table  are  obtained  : 

Table  IX. 


Calculated 

Calculated 

Obsened 

Height  of  Fall 
in  Inches. 

Maximum  Pres- 
sure in  Tons. 

Compression  in 
Inches. 

Compression  in 
Inches. 

60 

3.95 

0.234 

0.234 

54 

3.79 

0.224 

0.222 

48 

3.57 

0.212 

0.208 

42 

3.35 

0.199 

0.194 

36 

3.10 

0.184 

0.179 

30 

2.83 

0.166 

0.163 

24 

2.57 

0.148 

0.144 

18 

2.19 

0.120 

0.121 

12 

1.80 

0.091 

0.094 

6 

1.29 

0.053 

0.060 

"  Within  the  limits  of  the  experiments  it  may,  tlierefore,  I  tJiink,  be 
*    Vide  Royal  Engineer  Corps  Paper  X.,  vol.  xviii.,  published  1870,  and  dated 
September  27,  1869,  by  Lieutenant  T.   English,  R.E.,  "On  the  Statical  Pressuie 
produced  by  the  Impact  of  a  Falling  Weight." 


24  Submarine  Mining. 

assumed  that  the  greatest  pressure  produced  by  a  weight  falling  upon 
similar  cylinders  varies  as  the  square  root  of  the  height  from  whicli  it 
falls,  that  is,  directly  as  its  striking  velocity. 

"  In  the  explosion  of  a  torpedo,  assuming  the  variations  of  pressure 
to  be  transmitted  outwards  at  the  same  velocity  in  all  directions  from 
the  charge,  it  is  clear  that  the  velocity  of  any  particle  considered  to  lie 
on  the  surface  of  a  sphere,  of  which  the  charge  is  the  centre,  will  vary 

as  the  ?^^^^^  of  the  sphere,  that  is,  inversely  as  the  radial  distance 
volume  '^ 

from  the  charge." 

This  sentence  has  recently  been  more  fully  explained  to  the  author 
by  Major  English  as  follows  : 

Consider  a  thin  spherical  shell  with  centre  at  C  C  being  the  charge. 
Let  A  B  D  E  be  any  portion  of  it  bounded  by  lines  radiating  from  tlie 
charge.     Then,  assuming  water  to  be  incompressible,  and  the  maximum 


hydrostatic  pressure  due  to  the  explosion  to  be  ])  pounds  per  square 
inch,  the  pressure  on  A  E  will  be  p  x  surface  A  E,  tending  to  cause 
motion  outwards.  The  mass  of  water  set  in  motion  will  be  that  of  the 
volume  BCD.     By  the  equation  P  =  vif, 

p  X  surface  A  E=:vol.  B  C  D  x/, 

consequently /varies  as  -;-, ,  which  is  proportional   to   that  of   a 

sphere  of  which  the  charge  is  the  centre. 

Also  as  the  time  through  which  p  acts  is  the  same  at  any  distance 

from  c, 

surface 
v=ft,  and  also  vanes  as  ^^^^ 

In  the  above,  /=  acceleration,  or  increase  of  velocity  in  one  second. 

"  If  the  effect  on  copper  cylinders  be  considered  to  be  produced  by 
the  blow  of  an  uniform  weight  of  water  striking  them,  and  if  the 
maximum  pressure  produced  follows  the  law  already  shown  to  hold  good 
for  a  falling  weight,  and  varies  directly  as  the  striking  velocity,  it 
follows  that  tlie  maximum  pressure  per  square  inch  produced  by  the 
explosion  of  a  torpedo  is,  for  bodies  of  equal  resisting  power,  inversely 
as  their  radial  distances  from  the  charge. 

•'  From    the  exporiments  (October  and  December,  1873)  with  500  lb. 


Theoretical  Considerations. 


25 


charges  of  guu-cotton  it  appears  that  the  results  upon  similar  cylinders 
at  various  distances  were  as  follows  : 

Table  X. 


Letter                   ^3.^3.\  Distance 
Indicating'  Cylinder.      |  f^""  flU^''  *" 

Observed 

Calculated 
Pressure  in 

Pressure  Multi- 

Compression in 
Inches. 

Tons  per 
Square  Inch 

plied  by  Radial 
Distance. 

from  Table. 

f    ^ 

23 

0.055 

7.05 

162 

In   same  radial)    C 

30 

0.024  (bad) 

4.50 

135 

line      ...Id 

37 

0.020 

4.10 

152 

I   E 

44 

0.014 

3.50 

154 

Ditto.     .     .{    J 

30 

0.066 

8.20 

246 

60 

0.018 

3.80 

228 

G 

38 

0.047 

6.60 

251 

H 

45 

0.032 

5.40 

243 

"  The  results  observed  from  F  J  U  H  show  a  tolerable  accordance 
with  the  law  given  above,  and  although  cylinders  BODE  were 
arranged  along  the  bottom,  and  therefore  under  different  conditions  to 
the  others,  yet  they  agree  fairly  among  themselves. 

"Within  the  limits  of  the  experiments,  the  curve  of  which  the  com- 
pressions of  the  copper  cylinders  are  abscissae,  and  the  corresponding 
pressures  ordinates,  approximates  to  a  parabola  with  its  axis  on  the 
line  of  abscissaj.  Hence,  for  this  part  of  the  curve,  the  area  which 
represents  the  work  done  on  the  cylinders  varies  as  the  cube  of  the 
pressure,  that  is,  inversely  as  the  cube  of  the  radial  distance  from  the 
charge. 

"  Beyond  these  limits,  liowever,  and  under  greater  pressures,  the 
curve  diverges  altogether  from  the  parabolic  form,  and  this  law  would 
no  longer  hold  good." 

The  theory  explained  and  formulated  above,  viz.,  that  tlie  pressure 
produced  at  any  distance  from  an  explosion  varies  directly  as  the 
distance,  has  been  adopted  by  the  author  in  a  formula  to  be  discussed 
at  the  end  of  this  chapter,  a  term  being  added  to  express  the  high 
pressures  met  with  at  small  distances  from  the  charge.  As  stated  on 
page  15,  the  crusher  gauges  used  in  England  were  screwed  into  iron 
shot  or  shell  suspended  by  floats  and  attached  to  the  bottom  by 
sinkers ;  or  they  were  screwed  into  rings  which  were  fixed  to  sinkers, 
and  therefore  rested  on  the  bottom ;  or  they  were  secured  to  an  iron  or 
metal  ring  surrounding  a  small  charge  placed  in  the  c^tre,  as  in  the 
American  experiments ;  or  they  were  secured  to  the  side  of  a  vessel 
subjected  to  the  blow  of  a  submarine  mine  or  torpedo.  The  gauges  in 
the  shells  pointed  in  all  directions,  and  it  was  noted  that  when  such  a 
shell  was  placed  at  a  fair  distance  from  tlie  exploding  charge,  the  com- 


26  Submarine  Mining. 

pressions  in  all  the  gauges  were  not  unfrequently  alike,  and  seldom 
varied  greatly  inter  se. 

In  the  ring  experiments  both  in  England  and  America  the  compres- 
sions obtained  in  the  top  crusher  gauges  were  usually  greater  than  the 
compressions  obtained  on  the  gauges  in  the  same  horizontal  plane  as  the 
charge,  and  still  greater  than  the  compressions  in  the  bottom  gauges  of 
the  ring. 

This  difference  was  moreover  more  observable  when  the  ring  was 
near  the  surface  than  when  it  was  submerged  to  a  greater  depth, 
indicating,  apparently,  that  the  greatest  pi'essures  were  produced 
towards  the  lines  of  least  resistance. 

At  very  small  distances  the  results  are  abnormally  severe.  This  was 
observed  in  many  of  the  American  experiments  with  small  charges  in 
rings  fitted  with  gauges,  and  was  especially  observable  when  the 
higher  explosives  were  employed. 

As  before  stated,  the  large  pellets  in  some  experiments  appear  to 
have  been  compressed  by  more  than  one  blow,  frequently  by  two  severe 
blows  of  almost  equal  intensity,  and  then  by  a  series  of  smaller  blows. 
The  second  blow  may  be  due  to  the  reaction  from  the  bottom,  but  it  is 
not  easy  to  account  for  the  smaller  blows  following  it. 

Wlien  the  explosion  of  a  charge  takes  place  a  sphere  of  gas  is  formed 
at  an  enormous  pressure,  which  probably  varies  directly  as  the  charge 
and  as  the  intensity  of  action  of  the  explosive.  This  sphere  of  gas  ex- 
pands quickly  or  slowly  according  to  the  amount  of  resistance  opposed 
to  it,  as  shown  by  the  greater  height  to  which  the  water  is  thrown  by 
charges  exploded  near  the  surface,  a  smaller  mass  of  water  being 
driven  at  a  greater  height,  and  consequently  at  a  greater  initial 
velocity. 

Moreover,  the  crater  of  upheaval  increases  in  diameter  with  the 
submersion  of  the  charge  up  to  a  certain  limit,  the  work  being  expended 
in  moving  a  larger  mass  of  water  at  a  smaller  velocity.  The  sphere  of 
gas,  whatever  be  the  position  of  a  charge,  must  expand  more  rapidly  in 
the  direction  of  the  line  of  least  resistance  (L.L.R.),  and  in  so  expanding 
pushes  before  it,  with  immense  force,  the  mass  of  water  lying  in  and 
around  the  L.L.R.  If  a  vessel  happen  to  lie  in  or  near  to  this  L.L.E. 
she  must  receive  the  shock  due  to  the  vis  viva  of  the  whole  or  part  of 
this  water  in  motion,  and  she  succumbs  to  this  racking  blow,  or  resists 
it  according  to  her  strength.  If  the  L.L.R.  happen  to  pass  through 
the  ship's  side,  i.e.,  if  her  strength  offer  less  resistance  to  the  force  of 
the  explosion  than  the  inertia  of  the  water  between  that  part  of  the 
ship's  side  and  the  surface,  then  must  her  side  or  bottom  be  of  necessity 
l)lowii  in,  and  this  consideration  aloTie  shows  how  much  more  effective 


Theoretical  Considerations.  27 

an  explosion  must  be  when  directly  under  the  keel  of  a  vessel  than 
when  under  her  side.  Yet  the  initial  pressure  sustained  by  the  nearest 
portions  of  the  vessel  to  the  charge  is  the  same  in  these  two  cases, 
although  the  well-known  results  are  widely  difl'erent. 

If  the  history  of  submarine  explosions,  whether  in  war  or  peace,  be 
examined  to  present  date,  no  single  instance  will  be  found  in  which  an 
iron  vessel  possessing  a  skin  at  all  approaching  in  strength  that  of  the 
outer  skin  of  a  modern  warship  has  sustained  any  fatal  injury  from  an 
explosion  when  she  lay  outside  the  water  crater.  The  vessel  may 
receive  a  shock  that  discovers  weak  points  in  her  machinery  or  hull, 
but  if  sound,  and  properly  built,  she  will  apparently  receive  no  fatal 
injury  unless  subjected  to  the  blow  of  water  in  mass  driven  against 
her  at  high  velocity. 

Jt  is  extremely  probable  that  the  pressures  registered  in  crusher 
gauges,  placed  in  different  positions  with  reference  to  a  charge,  may 
assist  in  solving  the  problem  as  to  where  a  vessel  of  given  strength  is 
likely  to  receive  a  fatal  injury  from  such  charges.  They  enable  us  to 
measure  the  pressures,  but  we  cannot  measure  the  dimensions  of  the 
globes  of  gas  suddenly  formed  (except  very  roughly  by  the  craters  made 
in  mud),  nor  can  we  directly  measure  the  velocity  at  which  the  water  is 
driven  against  a  ship's  side  or  bottom.  Moreover,  inasmuch  as  it  is 
impossible  to  try  each  kind  of  explosive  against  a  target  representing 
an  ironclad,  crusher  gauge  experiments  became  convenient  methods  of 
comparing  the  comparative  intensity  of  action  of  different  explosives. 
But  crusher  gauge  experiments  must  be  received  with  great  caution,  as 
well  as  any  formulae  deduced  from  them.  The  mathematical  exactitude 
which  seems  to  be  allied  with  a  formula  may  do  more  harm  than  good 
unless  it  be  verified  by  target  experiments. 

A  collection  of  facts,  as  recorded  from  actual  target  experiments, 
must  be  the  first  thing  to  examine  carefully,  and  the  tabulated  results 
already  given  are  most  useful  in  this  direction.  In  short,  when  the 
limits  of  submarine  mining  experiments  on  which  an  empiric  formula  is 
based  are  not  exceeded,  it  is  more  likely  to  be  trustworthy  than  one 
which  is  founded  on  theoretical  considerations,  because  our  knowledge 
of  what  occurs  during  a  subaqueous  explosion  is  at  present  so  re- 
stricted. 

The  experiments  carried  out  in  America  were  mostly  with  small 
charges,  and  are  chiefly  useful  in  giving  an  indication  as  to  the  relative 
intensity  of  action  of  various  explosives,  as  registered  by  crusher 
gauges  placed  at  small  distances  from  the  charges. 

The  careful  and  scientific  investigation  of  the  theory  of  subaqueous 
explosions    which    General    Abbot   has    made,    rests    mainly    on    such 


28  Submarine  Mining. 

experiments,  and  his  deductions  must  therefore  be  accepted  with  caution. 
They  are  not  always  corroborated  by  the  results  of  experiments  with 
larger  charges,  as  was  shown  in  some  of  the  explosions  fired  against 
the  Oberon,  and  against  the  target  ship  at  the  Carlskrona  experiments. 

Every  expert  should  study  General  Abbot's  book,  "  Submarine  Mines, 
1881,"  with  the  greatest  attention,  but  it  is  probably  out  of  the  reach  of 
many  who  will  read  these  papers,  and  a  summary  of  his  investigations 
and  formulae  will  therefore  be  given. 

The   most   important   deductions   from    the   numerous    experiments 
carried  out  by  General  Abbot  in  America  are  as  follows : 
Let 
W  =  the  mechanical  work  done  by   a  submarine  explosion,  expressed  in  foot- 
pounds per  square  inch  of  surface  exposed  to  the  shock. 

P  =  intensity  of  action,  or  sudden  pressure  in  pounds  per  square  inch  of  above 
surface  exposed. 

C  =  weight  of  charge  in  pounds. 

D  =  distance  in  feet  from  centre  of  charge  to  above  surface. 

S  =  submersion  of  centre  of  charge  in  feet. 

N  =  number  of  fuzes  in  the  charge,  distributed  uniformly. 

R  =  radius  of  a  sphere  equal  in  volume  to  the  explosive  fired  by  each  fuze. 

N.B. — With  two  fuzes  attached  to  12  ft.  of  lightning  fuze  coiled  in  a  mine 

Q 

charge,  experiment  proved  that  R  =  — — . 

a  =  angle  in  degrees  at  centre  charge  between  the  vertical  downwards  and  the 

line  of  direction  of  the  blow  examined. 
E  =  value  to  be  found  by  trial  for  each  explosive  compound. 
M  =  ditto  for  each  explosive  mixture. 

Then  for  explosive  compounds  : 

„,^0.21(a  +  E)C  ,,> 

(D  +  0.01)2.i  •  ■  ■     ^  ' 

and 

p_    7/6636  (a +  E)CV  -„v 

\/  y(D  +  O.Olf-'j       '  '  '     ^' 

Also  for  explosive  mixtures  : 

P^     7/  MS^'^C'^Y        •  •  •     ^^^ 

The  following  considerations  were  also  evolved.  Remarks  on  them 
by  tlie  present  author  are  bracketted  as  being  more  convenient  tluin  a 
number  of  foot-notes. 

Other  variables  may  be  mentioned,  such  as  the  depth  of  water  under 
the  charge,  the  character  of  the  bottom,  &c. ;  but  as  the  experiments  at 
Willet's  Point,  where  the  bottom  was  soft  mud,  appeared  to  indicate 
that  these  jiad  no  sensible  influence  on  the  results,  they  are  neglected. 


Abbot' )i  Equations.  29 

[Tliis  is  not  borne  out  by  experiments  elsewliere.  For  instance,  in  the 
Oberon  experiments  with  500  lb.  charges  of  gun-cotton  it  was  con- 
sidered that  the  effects  of  No.  5  experiment  were  no  greater  than  those 
of  No.  4,  and  that  the  effects  of  No.  6  were  decidedly  greater  than 
those  of  No.  5.  It  is  considered  by  some  experts  that  large  ground 
mines  are  more  effective  than  equal  charges  buoyed  up  considerably 
from  the  bottom  by  nearly  30  per  cent.,  but  this  is  very  doubtful.] 
Again,  the  nature  of  the  priming  might  be  expected  to  influence  the 
force  produced  by  the  explosion  of  an  explosive  mixture ;  "  but  the 
results  with  gunpowder  appear  to  be  sensibly  the  same  whether  the 
priming  consists  of  fulminating  mercury,  safety  compound,  or  gun- 
powder." [In  an  addendum  General  Abbot  draws  attention  to  the 
announcement  made  by  Messrs.  Roux  and  Sarran  so  long  ago  as  1874, 
that  they  had  succeeded  in  obtaining  from  musket  powder  more  than 
four  times  the  usual  explosive  force  by  the  use  of  primers  so  large  as  to 
apply  a  detonating  shock  to  all  parts  of  the  charge.  This  has  not  been 
verified  by  experiment.]  In  framing  a  general  formula  for  submarine 
explosions  it  may  fairly  be  assumed  that  the  available  energy  developed 
by  the  detonation  of  higher  explosives  varies  directly  as  0.  With 
mixtures,  however,  the  case  is  different,  because  with  a  weak  envelope 
some  of  the  powder  is  driven  into  the  water  unexploded,  and  with  a 
strong  envelope,  although  this  loss  is  minimised,  energy  is  consumed  in 
the  rupture  thereof.  With  mixtures  therefore  the  energy  may  be  said 
to  vary  as  C''.  "In  a  perfectly  incompressible  fluid,  the  total  energy 
transmitted  through  it  from  iiiolecule  to  molecule  must  be  equal  upon 
every  spherical  surface  enveloping  the  explosive  as  a  centre.  In  other 
words,  the  energy  at  any  point  must  be  inversely  proportional  to  the 
square  of  the  distance  of  that  point  from  the  centre  of  the  charge. 
Water,  however,  is  not  a  perfectly  incompressible  fluid.  Moreover,  a 
formula  framed  upon  the  supposition  that  the  energy  varies  only  as  a 
power  of  D  would  indicate  an  infinite  energy  for  zero  distance.  For 
these  reasons  the  function  for  distance  should  take  the  form  (D  +  A)'' 
in  which  A  is  a  small  constant,  and  in  which  q  must  always  be 
nearly  equal  to  2.  This  function  of  course  enters  the  formula 
for  W  in  the  denominator.  [It  would  appear  from  Major  English's 
remarks,  already  given,  that  the  equation  connecting  the  distance 
with  the  mechanical  work  done  cannot  be  expressed  in  so  simple  a 
manner  for  all  distances;  and  if  the  limits  be  confined  to  those 
which  are  of  practical  value,  that  the  exponent  is  more  nearly  3  than 
2.]  The  effect  of  increasing  S  is  to  increase  the  fluid  pressure  round  C, 
and  therefore  to  increase  the  resistance  to  the  formation  of  the  globe  of 
gas  when  C  is  exploded.     A  function  S*  in  the  numerator  satisfies  these 


80  Submarine  Minivg. 

conditions.     Again,  when  K  =  U  C  =  0.-.  K' placed  in  the  denominator 
will  fulfil  the  needful  conditions  for  that  quantity. 

"  The  probable  action  of  the  forces  developed  by  a  subaqueous  ex- 
plosion indicate  that  the  normal  line  of  maximum  intensity  will  be 
directed  upward,  and  of  minimum  intensity  downward.  A  function  of 
the  form  (a  +  E)'  in  the  numerator  will  fulfil  these  conditions." 

[If  this  should  satisfy  the  conditions  of  various  submarine  explosions, 
as  regards  E  E',  ifec,  for  different  explosives,  it  evidently  gives  an 
extremely  high  relative  value  to  the  higher  explosives,  i.e.,  those  in 
which  E  is  large  as  compared  with  a,  and  as  compared  with  E'  E",  <fec., 
for  other  and  lower  explosives.  The  question  arises  do  they  possess 
this  high  relative  value,  when  for  instance  employed  in  large  charges 
acting  at  a  distance  ?  They  do  possess  it  when  examined  for  energy 
developed  at  small  distances  from  the  charge,  and  the  values  for  E  E', 
(fee,  have  been  found  by  an  examination  of  these  actions,  i.e.,  by 
crusher  gauge  records  on  3  ft.,  4  ft.,  and  5  ft.  rings  surrounding  small 
charges.  An  examination  of  the  American  experiments  shows  that 
the  crusher  gauge  experiments  at  increased  distances  were  apparently 
only  carried  out  with  one  explosive,  dynamite.  In  these  the  gauges 
were  fixed  to  an  iron  crate  or  framework,  so  that  the  most  distant 
gauges  were  25^  ft.  from  C,  and  the  latter  was  gradually  increased  up  to 
100  lb.  dynamite,  the  pressure  per  square  inch  thereby  produced  being 
recorded  as  3088  lb.  Also  there  were  a  few  experiments  with  large 
charges,  in  which  crusher  gauges  were  used  at  greater  distances ;  but 
they  were  placed  on  the  bottom,  and  the  blows  reflected.  Experiments 
in  England  proved  that  the  effects  in  crusher  gauges  so  situated  were 
considerably  less  than  on  similar  gauges  fixed,  even  to  movable  objects, 
but  buoyed  up  from  the  bottom.  A  formula  therefore  w  hich  satisfied 
the  pressures  re'^orded  in  the  former  would  fail  entirely  to  account  for 
the  much  higher  pressures  recorded  in  the  latter.] 

General  Abbot's  formula  for  the  most  general  case  of  a  subaqueous 
explosion  then  takes  the  form  : 

^y_K(a  +  E)'  S^C^ 
(D  +  A)?R= 

K  being  a  constant  varying  with  the  nature  of  the  explosive. 

Lengthy  calculations  based  principally  on  a  number  of  crusher  gauge 
experiments  with  small  charges  evolved  from  this  general  equa- 
tion the  three  special  equations  already  given  and  numbered  (1), 
(2),  (3). 

By  equation  (1)  P  varies  directly  as  the  two-thirds  power  of  C,   and 

4  2 
inversely  as  tlie     '    =1.4  power  of  D,  whatever  may  be  the  direction  of 


M  = 

790 

M  = 

20 

M  = 

59 

M  = 

1,554 

M  = 

3,331 

Abbot's  Conclusions.  31 

the  object  or  target.      Also  P  varies  directly  as  the  two-thirds  power   of 
E  when  the  target  is  over  the  charge,  a  then  being  0. 

By  equation  (2)  W  varies  directly  as  C  and  inversely  as  D-  nearly. 
Equation  (3)  refers  only  to  the  horizontal  plane  through  the  centre 
of  the  charge.  Hence  if  we  wish  to  compare  the  compounds  witli  tin; 
mixtures,  a  in  equations  (1)  and  (2)  must  =90  deg.  The  values  of  M 
for  different  explosive  mixtures,  found  after  a  large  number  of  experi- 
ments in  America,  are  : 

Table  XI. 
Mortar  powder    ... 

Mammoth  powder  

Cannon  powder 

Musket  powder 

Sporting  powder  (tine  orange  lightnuig) 

Safety    compound,    Oriental   Powder  Company,    a 

mixture  of  potassium  chlorate  and  gambier         ...     M=  13,383 

Applying  equation  (3),    let  us   find  P   when  0=100   lb.  safety   com- 
pound, and  when  S  =  5  ft.,  and  D  -  10  ft.     Then  as  M  =  13,383, 
Log  P  =  S  (log  13,383  +  tV  log  5  +1.94  log  100  -  2  log  1 1  -  i  log  0.8) 
and 

P=:9842  Ih.  on  square  inch. 

Safety  compound,  although  so  powerful  as  compared  with  the  other 
explosive  mixtures,  "  has  been  driven  from  the  market  by  the  nitro-com- 
pounds  which  have  been  proved  to  be  both  stronger  and  safer  to  handle." 

[It  may,  however,  sometimes  occur  that  officers  are  compelled  to  use 
gunpowder.  Its  effects  at  different  distances  are  consequently  calcu- 
lated further  on.] 

Before  leaving  this  part  of  the  subject  General  Abbot  noted  that : 

1.  The  strength  of  gunpowder  for  submarine  work  is  nearly  inversely 
proportional  to  the  size  of  the  grains. 

2.  Large  charges  of  gunpowder  are  less  wasteful  tlian  small  charges, 
because  a  smaller  proportion  of  the  charge  is  blown  into  the  water  un- 
burnt.     [This  depends  greatly  on  the  mode  of  ignition.] 

3.  A  strong  case  is  required  for  a  charge  of  gunpowder  for  a  similar 
reason. 

4.  No  advantage  is  obtained  by  the  employment  of  detonating  fuzes 
or  of  a  large  detonating  primer.     [Questionable.] 

5.  An  air  chamber  in  a  gunpowder  mine  placed  between  the  charge 
and  the  object  is  highly  advantageous,  because  it  directs  the  blow  and 
increases  the  effective  pressure  in  the  desired  direction. 

6.  An  excellent  way  to  ignite  a  large  charge  of  gunpowder  is  to  use 
two  fuzes  in  connection  with  some  lightning  fuze  coiled  away  in  the 
powder. 


82  Suhmao'ine  Mining. 


Detonating  Compounds  and  Mixtures. 
Before  examining  and  comparing  tlie  different  explosives  which  have 
been  tried  in  the  American  experiments  it  will  be  convenient  to  record 
some  of  the  more  important  general  conclusions  that  were  discovered 
during  the  American  series  of  experiments. 

1.  Submersion. — So  long  as  a  charge  is  submerged  to  an  extent  likely 
to  occur  in  practice,  the  results  on  a  target  are  not  affected  to  any- 
appreciable  extent.  In  other  words,  S  has  so  small  a  fractional 
exponent  as  to  become  practically  unity,  and  may  therefore  be  omitted 
as  a  multiplier  in  the  formula.  A  submersion  of  4  ft.  for  a  charge  of 
100  lb.,  and  4  ft.  per  100  lb.  for  larger  charges,  being  sufficient  to 
develop  the  full  effects  of  a  subaqueous  explosive  of  the  first  order. 

2.  A  thin  weak  envelope  gives  the  best  results.  [Just  the  reverse 
with  gunpowder,  as  already  noted.] 

3.  No  advantage  is  gained  by  the  use  of  more  than  one  detonator. 
[Again  different  to  gunpowder.] 

4.  The  energy  cannot  be  directed  by  the  employment  of  air  chambers 
in  the  mine.     [Again  different  to  gunpowder.] 

5.  An  air  space  not  exceeding  three  times  the  volume  of  the  charge 
complete  with  its  apparatus,  &c.,  has  no  prejudicial  effect.  [A  much 
larger  air  space  is  required  in  practice.] 

6.  The  mine  case  should  not  be  formed  of  compressible  material  that 
can  absorb  work  by  pulverisation,  such  as  wood  [which  differs  from  air 
in  not  again  giving  forth  the  energy  absorbed  in  its  compression]. 

Two-inch  wooden  cases  for  small  charges  of  dynamite  occasioned  a 
loss  of  effect  on  gauges  of  no  less  than  55  per  cent.  ;  with  dualin  the 
loss  was  47  per  cent.,  and  with  gun-cotton  40  per  cent. 

7.  Some  explosive  compounds  are  liable  to  sympathetic  explosion. 
Dry  is  much  more  sympathetic  than  wet  gun-cotton.  Compacted 
dynamite  is  more  sympathetic  than  loose  dynamite.  Abbot's  equation 
for  finding  the  distance  of  sympathetic  explosions  under  water  is  : 

where  B  is  a  value  found  by  experiment  with  eacli  explosive  and 
description  of  envelope,  and  D  is  the  distance  in  feet  from  a  charge 
C  lb.  at  which  sympatlietic  explosion  will  occur.  With  compacted 
dynamite  and  thin  tin  envelope  B  =  20. 

8.  "  The  considerable  effect  upon  the  numerical  value  of  P  produced 
by  varying  the  direction  of  the  line  of  action  in  vertical  plane-s  passing 
through  the  charge  and  vessel,  emphasises  the  importance  of  placing 
the  former  under  the  latter  if  possible. 


General  Abbot's  Vietus.  33 

9.  "  The  small  exponent  of  C  (only  |)  in  the  value  of  P  shows  that 
with  a  given  weight  of  explosive  many  moderate  charges  block  a 
channel  more  efTectually  than  a  few  large  ones.  Thus  a  mine  containing 
500  lb.  is  only  2.9  times  as  eflfective  as  one  of  100  lb."  [The  exponent 
of  C  in  the  formula,  and  the  theory  resting  upon  it,  are  equally  open  to 
doubt.] 

10.  Explosives  which  are  compacted  are  more  difficult  to  detonate 
with  a  fuze  than  those  which  are  in  a  looser  state.  Thus  loose  dyna- 
mite, even  if  in  the  frozen  state,  can  be  always  detonated  by  15  grains 
of  mercurial  fulminate  in  a  copper  capsule,  whereas  compacted  dyna- 
mite in  the  frozen  state  cannot.  It  is  due  to  the  larger  surface  exposed 
to  the  flame  and  shock  of  the  fuze  when  the  dynamite  is  loose.  [It  is 
to  be  observed  that  the  compacted  dynamite  is  the  most  sensitive  to 
sympathetic  detonation,  and  although  this  at  first  sight  seems  contra- 
dictory, it  may  be  accounted  for  similarly,  a  larger  amount  or  surface  of 
dynamite  being  then  in  contact  with  the  envelope  through  which  the 
detonation  is  transmitted.] 

11.  Some  of  the  compounds  are  equally  powerful  when  wet  and  fully 
exposed  to  the  sea  water  as  when  dry.  [General  Abbot  claims  that 
this  fact  was  discovered  by  him  before  wet  gun-cotton  was  first 
detonated  in  England,  late  in  the  year  1872.] 

12.  Some  of  the  compounds  are  both  safe  and  efiective  when  in  the 
frozen  state,  and  are  not  deteriorated  when  subjected  to  great  dif- 
ferences of  temperature  in  store. 

[The  coefficients  for  the  intensity  of  action  for  the  difiierent  explosives 
as  stated  may  probably  be  accepted  as  giving  fairly  accurate  results 
when  applied  to  General  Abbot's  formulae  (1)  and  (2)  within  the  limits 
of  the  experiments  on  which  they  are  based.  But  the  pressures  calcu- 
lated for  longer  distances  by  equation  (2)  do  not  agree  with  the  results 
of  the  experiments  made  in  this  country.  For  instance,  the  500  lb. 
experiments  in  October  and  December,  1873,  already  tabulated  in  the 
quotation  from  Major  English's  memorandum,  show  that  the  pressures 
vary  within  the  limits  of  those  experiments  inversely  as  the  distances, 
and  not  inversely  as  the  1.4  power  of  the  distances  as  suggested  by 
General  Abbot.] 

The  formula  proposed  by  the  writer  will  be  examined  in  a  subsequent 
page. 

It  is,  of  course,  important  that  correct  views  should  be  held  con- 
cerning the  manner  in  which  submarine  explosions  act,  in  order  that 
the  formulaj  required  for  determining  the  various  effects  produced  by 
difi'erent  explosives  and  charges  at  different  distances,  and  under 
different  conditions,  may  be  approximately  determined. 
I) 


84  Submarine  Mining. 

An  examination  of  experiments  will  often  be  sufficient  to  guide 
practice  without  any  formulae;  but  as  new  explosives  come  on  the 
field,  and  fresh  conditions  become  involved,  a  correct  formula  becomes 
more  than  ever  necessary  if  the  mines  are  to  be  arranged  and  charged 
in  a  good  and  economical  manner.  Evidently  the  initial  pressure 
must  vary  as  the  quantity  of  gas  suddenly  generated  at  a  high  tem- 
perature. 

It  would  be  extremely  difficult  to  estimate  the  quantity  of  permanent 
gas  suddenly  produced  and  the  temperature  of  explosion,  and  still  more 
difficult  to  introduce  a  function  for  increased  effect  under  water  due  to 
the  greater  or  less  sudden  action  of  any  given  explosive  as  compared 
to  another  explosive  ;  but  experiments  have  given  some  fairly  accurate 
data  on  the  relative  intensity  of  action  under  water  of  different  explo- 
sives, and  in  all  probability  this  intensity  of  action  includes  in  the 
most  practical  form  both  the  gas  suddenly  generated  and  its  tempe- 
rature, as  well  as  the  relative  velocity  of  detonation,  and  perhaps  other 
important  but  complicated  matters  which  surround  the  subject  of 
subaqueous  explosions. 

Assuming  that  the  maximum  pressure  produced  by  an  explosion 
varies  directly  as  the  intensity  of  action  of  the  explosive  as  com- 
pared with  other  explosives  in  experiments  made  with  small  charges 
acting  under  water  at  small  distances,  it  is  evident  that  it  also  varies 
as  the  quantity  of  explosive  used  in  a  charge,  or  as  0  x  I. 

Adopting  the  ruling  idea  set  forth  in  Major  English's  memorandum 
already  quoted,  viz.,  that  between  certain  limits  the  pressure  produced 
by  the  explosion  of  a  torpedo  varies  inversely  as  the  distance  of  the 
object,  we  arrive  at  the  conclusion  that  the  pressures  vary  approxi- 
mately as X  constant. 

C  being  the  weight  in  pounds  of  explosive  in  charge. 

I  being  the  relative  intensity  of  action  of  the  explosive  :  dynamite  No.  1  being 

the  unit. 
D  being  the  distance  in  feet  from  the  centre  of  the  charge  to  an  unscreened 

crusher  gauge. 

The  pressure  per  square  inch,  as  recorded  in  gauges,  being  found  for 
various  distances,  and   charges  of  explosives,  an  examination  proved 

C  I 

that  at  moderate  distances  the  equation  P=    ^-  x  constant  was  fairly 

well  satisfied  when  constant  =  9. 

But  this  ecjuation  does  not  agree  with  practice  at  small  distances. 

Close  to  the  charge,  say  within  20  ft.,  different  conditions  obtain, 
and  it  therefore  becomes  necessary  to  add  to  the  above  simple  form  of 


Formula  noxo  Pro2)osed. 


35 


and  that  it  should  take  the  form 


constant.     After  much  labour 


equation  for  pressure  a  term  which  would  satisfy  approximately  tlie 
greatly  increased  pressures  recorded  at  the  smaller  distances. 

It  appeared  probable  that  this  term  must  also  vary  directly  as  C  x  I, 

cj: 

the  writer  found  that  fairly  accurate  results  are  obtained   in  the  hori- 
zontal plane  when  x  =  3,  and  the  constant  =  225. 
The  equation  consequently  becomes  : 

Applying  this  equation  to  some  of  the  American  experiments  with 
dynamite  charges,  and  to  some  of  the  English  experiments  with  gun- 
cotton  charges,  it  will  be  seen  that  it  gives  pressures  agreeing  more 
closely  with  the  pressures  recorded  on  the  crusher  gauges  than  do  the 
pressures  computed  by  General  Abbot's  formula. 
Table  XII. 


225  C  I 


(4) 


P  Pounds  per  Square  Inch. 

Calculated. 

c. 

I. 

D. 

Observed 

Remarks. 

on 

Gauges. 

Abbot's 
Formula. 

Formula 

now 
Proposed. 

lb. 

ft. 

1 

100 

1.62 

8000 

7,555 

7853 

Dynamite. 

10 

100 

3.62 

8500 

11,432 

7458 

^ 

50 

100 

25.5 

1840 

2,181 

1835 

100 

100 

70 

1141 

842 

1293 

" 

100 

100 

25.5 

3088 

3,461 

3671 

200 

100 

SO 

1365 

1,109 

2260 

Crushers    on    a    ground 
mine.    Blow  apparently 
deflected   by    the   bot- 
tom. 

The  American  experiments  proved  that  the  mean  pressures  in  the 
vertical  plane  were  greatest  towards  the  zenith  and  least  towards  the 
nadir,  also  that  these  differences  varied  inversely  (nearly)  as  the 
intensity  of  action  of  the  explosive.  The  pressures  computed  by 
the  equation 

D    V         DV 

are  for  the  horizontal  plane.  If  the  target  be  above  or  below  this  plane 
the  pressures  should  be  increased  or  decreased  by  the  following  per- 
centages (e)  according  to  the  explosive  employed  : 

For  gun-cotton,  dynamite  No.  1,  and  other  explosives  whose  intensity 
of  action  is  about  100,  add  or  deduct  20  per  cent,  at  the  vertical,  and 
d2 


Submarine  Mining. 


proportionately  smaller  amounts  for  other  angles  smaller  than  90  cleg, 
from  the  horizontal  plane. 

For  blasting  gelatine,  whose  intensity  of  action  is  about  142,  add  or 
deduct  12  per  cent,  at  the  vertical,  and  smaller  amounts  proportional 
to  smaller  angles.  And  so  with  other  explosives,  as  shown  in  the 
following  Table  for  I  and  e.  For  gunpowder  the  writer  takes  I  =  25 
and  e  =  35. 

The  above  assumes  that  the  charges  are  sufficiently  tamjjed  or  sub- 
merged, say  by  at  least  4  ft.  per  100  lb.  of  explosive  in  the  charge. 
When  submerged  to  a  smaller  extent  the  pressures,  especially  for 
gunpowder  charges,  cannot  be  computed,  so  much  of  the  force  being 
expended  in  driving  water  uselessly  into  the  air.  For  a  similar  reason 
the  computed  pressures  form  no  indication  of  the  results  when  a  charge 
is  placed  close  to  a  weak  vessel — in  this  case,  however,  it  is  most 
usefully  employed. 

If,  therefore,  P  be  the  pressure  in  pounds  per  square  inch  on  a 
target  in  the  vicinity  of  the  submarine  explosion  of  a  charge  containing 
0  lb.  of  any  explosive  whose  intensity  of  action  under  water  is  I  ; 
then  if  the  target  and  charge  be  in  the  same  horizontal  plane  at 
distance  D  ft.  apart, 

P.9CJ/^^25N      .         .         .         , 

and  if  the  target  be  out  of  the  horizontal  plane, 

D  \  B-J  \  90  100/ 
(B  being  the  angle  between  the  line  joining  the  centre  of  the  charge  and 
target  and  the  horizontal  plane,  and  e  being  the  percentage  for  the 
particular  explosive  used,  plus  if  target  be  above  horizontal  plane 
through  charge,  minus  if  below.     The  values  taken  for  I  and  for  e  are  : 

Table  XIII. 


(4) 


(5) 


Description  of  Explosive.            I. 

e. 

Blasting  gelatine 

Forcite         ,,       

(Jelatinc  dynamite  No.  1 

Dynamite  No.  1 

Gun-cotton         

Gunpowder         

142 
133 
123 
100 
100 
25 

12 
14 
16 
20 
20 
35 

Applying  this  equation  (5)  to  the  500  lb.  gun-cotton  experiments 
already  quoted  in  Major  English's  memorandum,  and  comparing  the 
results  with  the  pressures  calculated  by  General  Abbot's  formula,  the 
following  pressures  are  obtained,  again  pointing  to  equation  (.">)  being 
more  correct  than  equation  (2). 


FormulcB  Govipared. 


37 


Table  XIV. 


■■ 

D. 

P  Pounds  per  Square  Inch. 

c. 

Observed 

on 
Gauges. 

Abbofa 
Formula. 

Formula  now 
Proposed. 

Rhmarks. 

lb. 

500 

500 
500 
500 
500 
500 
500 
500 

ft. 

30 

38 
45 
60 
23 
30 
37 
44 

18,368  1 

14,784  -[ 
12,096  I 
8,512  { 
15,792  1 

9,184  j 
7,840  1 

a=  130  deg. 

8,821 

a  =  143  deg. 

6,509 
a  =  150  deg. 

5,210 
a  =130  deg. 

3,344 
a  =  90  deg. 

11,691 
a  =  90  deg. 

8,060 
a  =  90  deg. 

6,010 
a  =  90  deg. 

4,716 

3= +40  deg. 
16,791 

j3=+53deg. 

13,494 
B=  +60  deg. 

11,460 
,3= +40  deg. 

8,224 
/3  =  0deg. 

20,543 
^  =  Odeg. 

15,420 
/3  =  0deg. 

12,405 
|3  =  0deg. 

10,330 

Gun-cotton.      English 
experiments,      1873. 
Crushers      fixed     in 
shells,   buoyed   from 
the  surface. 

I  =  100   considered    a 
truer  value  than   87 
for  gun-cotton. 

The  gauges  in  these 
four  were  fixed  to 
sinkers  on  the  ground. 

Blow  apparently  de- 
flected by  the  bottom. 

*  Rejected  as  a  bad  result. 

An  inspection  of  the  analysis  of  the  Oberon  experiments  and  of  the 
pressures  now  calculated  by  the  above  formula  shows  that  a  modern 
ironclad  will  receive  a  fatal  injury  if  she  be  situated  so  that  her  outer 
skin  occupies  the  position  where  crusher  gauges  should  record  a  pres- 
sure P  of  about  12,000  lb.  (5^  tons)  on  the  square  inch. 

It  will  consequently  be  instructive  to  calculate  the  charges  of 
different  explosives  which  are  required  to  produce  this  result  at 
different  distances. 

in  horizontal  plane.     Consequently 

r  =  ^  /    ^M 

9  1    \D-+25/ 
from  which  the  following  values  for  the  charge  in  pounds  are  found  for 
the  different  explosives  at  the  distances  given  in  the  Table  : 
Table  XV. 


Distances  in  feet 

2.5 

5          10 

Charges  in  poi 

1 

20 

inds  w 

30 
ienP  = 

40 
12,000. 

50 

1  = 

Description  of  explosive. 

Blasting  gelatine 

Forcite 

Gelatine  dynamite 

Dynamite  and  gun-cotton 

Gunpowder         

lb. 
4.7 
5.1 
5.4 
6.6 
26.4 

lb. 
23.5 
25 
27 
33 
132 

lb. 

75 
80 
87 
107 
428 

lb. 
177 
188 
196 
251 
1004 

lb. 
274 
293 
316 
389 
1556 

lb. 

369 

395 

427 
525 
2100 

lb. 
465 
496 
537 
660 
2640 

142 
133 
123 
100 
25 

38 


Submarine  Mining. 


These  results  are  plotted  on  the  first  diagram,  wliich  is  useful  for 
quickly  finding  the  charge  of  either  of  the  named  explosives  wliich  is 
requii-ed  to  give  a  fatal  blow  to  a  modern  ironclad  at  any  intermediate 
distance. 


1 

Ola„ 

■van 

ram  shewirty  I'lnss    oF preiiure 
WO  /fci.  on  a"  produced  ty 
gus  charges  of  different     ' 
ysiiea   when  used  os  subn.a- 
m,nes    calculated  from  e^ua. 

/ 

.tiona 

wo 

1 

Ci/ 

/ 

1 

/ 

4 

r. 

1 

' 

'>/p^ 

^y 

./ 

^ 

i 

^^^ 

/ 

/^ 

' 

/ 

/ 

1/ 

^ 

V               J 

< 

' 

A  large  number  of  experiments  were  made  witli  dynamite  at  Willet's 
Point,  and  it  will  be  convenient  to  compare  graphically  the  dynamite 
curves  for  different  pressures  as  calculated  from  General  Abbot's 
formula  for  P,  wliich  was  based  upon  these  experiments.  The  curves 
are  shown  on  the  second  diagram,  and  they  can  be  adapted  to  other 
explosives  whose  relative  intensity  of  action  is  known,  by  using  the 
simi)le  proportion 

V  :  I"  :  :  I  :  I', 
I   for  dynamite  being   100   aiid    1'   the   relative   intensity   of   another 
explosive. 

In  a  similar  manncM-  each  curve  ran  be  a(l:ii)((Ml  to  another  oxjilosive. 


Formidcti  Plotted  Graphically. 


39 


Thus  to  adapt  the  curve  marked  12,000  to  blasting  gelatine  we  have 
12,000  :  X  ::  100  :  142.  Hence  a;  =  17,040,  or  the  12,000  lb.  curve  for 
dynamite  becomes  the  17,000  lb.  curve  for  blasting  gelatine,  and 
similarly  for  the  other  curves  on  the  diagram. 

An  examination  of  these  curves  will  show  that  the  charges  of 
dynamite  and  of  blasting  gelatine  required  to  give  a  pi-essure  P  =  6000 
at  various  distances,  are  as  follows,  when  P  =  6000  as  calculated  by 
Abbot's  formula,  such  pressure  being  considered  by  him  as  sufficient  to 
fatally  injure  a  man-of-war  as  strong  as  the  Hercules  : 
Table  XVI. 


Distance  D 

Blasting  gelatine 
Dynamite 


ft 

5 

10 

20 

.SO 

11) 

4 

17 

67 

160 

n 

32 

127 

321 

40 
311 
587 


ts  aF  equal 

'of  Dynamite  U  of  BloslSntj  Cehtme 
calculated  from  Ge/^'Abbots  formula 


Taking  into  consideration  the  nature  of  an  ironclad's  double  bottom, 
the  charges  for  small  distances  derived  from  General  Abbot's  forniula 
appear  to  be  incapable  of  producing  the  damage  required, 


40 


Submarine  Mining. 


When  P  =  12,000  as  calculated  by  the  author's  formula,  such  pres- 
sure being  considered  by  him  as  necessary  to  insure  a  fatal  injury  to  a 
modern  man-of-war,  we  have  : 

Table  XVII. 


Distance  D 
Blasting  gelatine 
Dynamite 


ft. 

5 

10 

20 

30 

lb. 

2^ 

75 

177 

274 

" 

33 

107 

251 

389 

40 
369 
525 


These  charges  are  certainly  more  in  accordance  with  practice,  and 
witli  the  results  annved  at  by  numerous  experiments. 


41 


CHAPTER   IV. 
Examination  of  Different  Explosives. 

The  more  important  of  the  high  explosives  will  now  be  briefly  alluded 
to,  and  those  of  them  which  appear  to  be  best  suited  for  submarine  work 
will  be  discussed  minutely  afterwards. 

Dynamite. — 1  =  100.  I  being  the  relative  intensity  of  action  as  com- 
pared with  equal  weights  of  other  explosives.  Composition  =  75  per  cent, 
of  nitro-glycerine,  25  per  cent,  of  keiselguhr.  This  explosive  possesses 
so  many  advantages  that  it  has  been  adopted  by  the  American  Govern- 
ment for  their  submarine  mines,  but  it  is  now  contemplated  to  employ 
one  of  the  newer  explosives,  probably  blasting  gelatine.  Dynamite  will 
be  examined  again. 

Gun-Cotton. — 1=  100.*  Abel's  compressed  gun-cotton  or  nitro-cellu- 
lose  possesses  so  many  advantages  that  it  has  been  adopted  by  our 
Government  and  by  several  of  the  European  Governments  for  sub- 
marine mining.     It  will  be  examined  again. 

Dualin. — I  =  lll.t  Composition  =  80  percent,  nitro-glycerine  and 
20  per  cent,  nitro-cellulose.  Best  form  believed  to  consist  of  nitro- 
glycerine absorbed  by  Schultze's  powder.  In  spite  of  its  great  power 
it  is  not  well  suited  for  submarine  work,  because  it  is  "dangerous 
when  frozen,  and  when  saturated"  (with  water)  "loses  half  its  normal 
strength"  (Abbot).     It  will  not  therefore  be  examined  further. 

Lithofracteur  (or  Rendrock). — 1  =  94.  Composition  =  40  per  cent, 
nitro-glycerine  and  40  per  cent,  sodium  or  potassium  nitrate,  13  per 
cent,  cellulose,  and  7  per  cent,  paraffin.  The  principal  absorbent  being 
soluble  renders  this  explosive  unsuitable  for  submarine  work.  Other 
forms  of  rendrock,  containing  some  more  and  some  less  nitro-glycerine, 
are  equally  open  to  this  objection  ;  and  those  with  a  larger  percentage 
of  nitro-glycerine  are  too  moist  to  be  safe  for  general  use.  Moreover, 
the  salts  used  as  absorbents  being  deliquescent,  cause  exudation  of 
nitro  glycerine  when  the  explosive  is  exposed  to  damp  during  storage. 
*  English  experiments  make  1=100,  or  slightly  >  100. 
t  Somewhat  similar  to  Abel's  glyoxilin  invented  1867. 


42  Submarine  Mining. 

Giant  Poioder. — I  =  83.  Composition  =  36  per  cent,  nitro-glycerine 
and  48  per  cent,  sodium  or  potassium  nitrate,  8  per  cent,  sulphur, 
8  per  cent,  resin,  coal,  or  charcoal.  It  is  weaker  than  rendrock,  and 
possesses  similar  disadvantages. 

Vulcan  Powder. — I  =  82.  Composition  =  35  per  cent,  nitro-glycerine 
and  48  per  cent,  sodium  nitrate,  10  per  cent,  charcoal,  7  per  cent, 
sulphur.  It  is  weaker  than  rendrock  or  than  giant  powder,  and  is  open 
to  the  same  objections. 

Mica  Powder. — I  =  83.  Composition  =  52  per  cent,  nitro-glycerine  and 
48  per  cent,  powdered  mica.  Its  strength  as  compared  with  otlier 
explosives  of  a  similar  character,  is  low. 

Nitro-Glycerine. — 1  =  81.  This  value  for  intensity  of  action  under 
water,  which  was  verified  by  repeated  experiments  in  America,  was 
most  unexpected.  After  laborious  and  careful  investigation.  General 
Abbot  considers  that  nitro-glycerine  is  too  quick  in  its  action  for  sub- 
marine mining.  He  fully  acknowledges  that  pure  nitro-glycerine  is 
more  powerful  than  dynamite  for  rock  blasting.  But  water  is  slightly 
compressible ;  and  in  order  to  obtain  the  best  results,  he  thinks  that  a 
certain  minute  fraction  of  time  is  required  in  the  development  of  the 
full  force  of  the  explosion.  If  this  explanation  be  correct  it  may 
account  for  the  superior  power  of  wet  over  dry  gun-cotton  when  used 
under  water.  It  also  explains  the  high  coefficient  given  to  blasting 
gelatine,  which  "  is  less  quick  and  violent  in  its  action  than  dynamite, 
although  stronger."     {Vide  circular  of  manufacturers.) 

Hercules  Powder.  1  =  106.  Composition  =  77  per  cent,  nitro-glyce- 
rine and  20  per  cent,  magnesium  carbonate,  2  per  cent,  cellulose,  1  per 
cent,  sodium  nitrate.  Unsuitable  for  submarine  mining,  because  the 
absorbents  are  soluble. 

Electric  Poioder. — I  =  69.  Composition  =  33  per  cent,  nitro-glycerine, 
and  rest  unknown.  Weak,  as  compared  with  other  nitro-glycerine 
explosives. 

Desiynolle  Powder. — 1  =  68. — Composition  =  50  per  cent,  potassium 
picrate,  50  per  cent,  potassium  nitrate.  Dangerous,  sensitive  to  fric- 
tion, weak. 

Brugere  or  Picric  Powder. —  I  =  80.  Composition  =  50  per  cent. 
ammonium  picrate,  50  per  cent,  potassium  nitrate.     Safe,  but  weak. 

Tonite. — I  =  85.  Composition  =  52.5  per  cent,  of  gun-cotton,  47.5  per 
cent,  of  nitrate  of  baryta.  There  are  two  varieties  of  this  explosive, 
one  dry,  in  compacted  cartridges,  the  other  damp,  in  bulk.  It  will  be 
examined  again. 

Explosive  Gelatine,  1881. — 1  =  117.  Composition  =  89  per  cent,  nitro- 
glycerine and  7  per  cent,  nitro-cotton,  4  per  cent,  camphor. 


Different  Explosives  Compared.  43 

Blasting  Gelatine,  1884. — I  =  142.  Composition  =  92  per  cent,  nitro- 
glycerine and  8  per  cent,  nitro-cotton.  This  explosive  is  probably  the 
best  for  submarine  mining,  and  will  be  examined  minutely  presently. 

Atlas  Powder  (A). — I  =  100.  Composition  =  75  per  cent,  nitro-glyce- 
rine  and  21  per  cent,  wood  fibre,  2  per  cent,  magnesium  carbonate, 
2  per  cent,  sodium  nitrate. 

Atlas  Powder  (B). — I  =  99.  Composition  =  50  per  cent,  nitro-glycerine 
and  34  per  cent,  sodium  nitrate,  14  per  cent,  wood  fibre,  2  per  cent, 
magnesium  carbonate. 

As  regards  A,  it  would  seem  to  possess  no  advantage  over  ordinary 
dynamite,  and  the  2  per  cent,  of  sodium  nitrate  is  objectionable,  as  it  is 
deliquescent.  As  regards  B,  it  would  be  a  bad  e.x;plosive  for  submarine 
mining,  on  account  of  the  large  amount  of  sodium  nitrate.  The  power 
developed  by  this  explosive  is  high,  considering  the  percentage  of  nitro- 
glycerine. 

Jiidson  Powder  (5). — 1  =  78.  Composition  =  17.5  nitro-glycerine  and 
rest  unknown. 

Jiidson  Powder  (3  F). — I  =  G2.  Composition  =  20  per  cent,  of  nitro- 
glycerine and  53.9  per  cent,  sodium  nitrate,  13.5  per  cent,  sulphur, 
12.6  per  cent,  powdered  coal,  cannel. 

These  are  very  powerful  considering  the  small  amount  of  nitro- 
glycerine. Still  more  wonderful  are  the  results  obtained  from  the 
following  grade  of  Judson  powder,  in  which  only  5  per  cent,  of  nitro- 
glycerine is  employed,  and  which  costs  about  the  same  as  common 
blasting  gunpowder. 

Judson  Powder  (C  M) — T  =  44.  Composition  =  5  per  cent,  nitro- 
glycerine and  64  per  cent,  sodium  nitrate,  16  per  cent,  sulphur,  15  per 
cent,  powdered  cannel  coal.  This  powder  does  not  explode  when  struck 
by  a  bullet,  nor  when  fired  by  a  match,  and  although  weak  for  sub- 
marine mining  it  would  appear  to  be  eminently  suited  for  military 
land  mining  and  work  in  the  field.  This  grade  of  Judson's  powder 
would  perhaps  be  more  properly  classified  under  the  heading  of  explo- 
sive mixtures,  both  on  account  of  its  composition  and  its  strength, 
which  is  not  sufficient  to  enable  us  to  adapt  it  to  Abbot's  equations  in 
which  E  appears. 

Rackarock. — I  =  88.  Composition  =  77.7  per  cent,  potassium  chlorate, 
22.2  per  cent,  nitro-benzole  (insoluble  liquid) ;  also  made  in  other  pro- 
portions and  with  various  modifications  in  the  ingredients. 

This  explosive  is  one  of  the  Sprengel  class  "  which  are  non-explosive 
during  their  manufacture,  storage,  and  transport."  Their  peculiarity  is 
that  the  ingredients  are  kept  separated  until  just  before  use.  Until 
mixed,  they  cannot  be  exploded.     When  mixed  a  very  powerful  explo- 


44  Submarine  Mining. 

sive  is  produced.  A  3  oz.  primer  of  tonite  or  of  gun-cotton  is  required 
to  detonate  rackarock.  Tlie  mixture  is  said  to  be  stable,  but  the  experi- 
ments made  with  it  at  Willet's  Point  indicate  that  its  explosive  action  is 
not  constant,  probably  due  to  the  rough  method  in  which  the  two 
ingredients  are  mixed.  It  appears  to  be  inferior  for  submarine  mining 
work  to  gelatine  dynamite,  to  blasting  gelatine,  to  forcite  gelatine,  gun- 
cotton,  and  dynamite. 

Forcite  Gelatine.—I  =  133.  Composition  =  95  per  cent,  nitro-glyce- 
rine  and  5  per  cent,  cellulose  (un-nitrated).  This  explosive  is  claimed 
to  possess  certain  advantages  over  blasting  gelatine,  which  will  be  ex- 
amined presently.  As  regards  power  for  subaqueous  work  it  is  nearly 
as  high  as  "  blasting  gelatine." 

Gelatine  Dynamite  (No.  1). — 1  =  123.  Composition  =  65  per  cent,  of 
A  and  35  per  cent,  of  B.  A  =  97.5  per  cent,  nitro-glycerine  and  2.5 
per  cent,  soluble  gun-cotton  ;  B  =  75  per  cent,  potassium  nitrate,  24  per 
cent,  cellulose,  1  per  cent.  soda. 

This  explosive  does  not  appear  to  have  been  examined  by  General 
Abbot.  The  value  for  I,  as  given  to  the  author  by  the  manufacturers 
=  123,  blasting  gelatine  at  the  same  time  being  given  at  153,  but 
these  values  were  not  based  on  subaqueous  crusher  gauge  experiments. 
General  Abbot's  value  for  I  for  blasting  gelatine  =  142,  and  the  above 
value  for  I  is  found  from  the  proportion  153  :  142  ::  132  :  123  nearly. 
Gelatine  dynamite  (No.  1)  appears  to  be  a  suitable  explosive  for  sub- 
marine mining,  and  will  be  examined  again. 

Gelignite. — I  =  102,  specific  gravity  =  1.5.  Composition  =  56.5  per  cent, 
nitro-glycerine  and  3.5  per  cent,  nitro-cotton,  8  per  cent,  wood  meal,  32 
per  cent,  potassium  nitrate.  The  value  for  I  given  by  the  manufacturers 
(Nobel's  Explosive  Company,  Limited)  is  110,  and  is  not  based  on 
crusher  gauge  experiments  under  water.  The  value  for  I  given  above 
is  found  in  the  same  way  as  that  for  gelatine  dynamite.  Gelignite  is 
but  slightly  more  powerful  than  No.  1  dynamite,  and  as  it  possesses  32 
per  cent,  of  a  soluble  salt  its  employment  in  submarine  mining  cannot 
be  recommended. 

Melenite. — Composition  (?).  Very  little  as  yet  is  known  of  this  ex- 
plosive, but  it  is  believed  to  consist  of  fused  picric  acid  in  granules 
agglutinated  with  tri-nitro-cellulose  dissolved  in  ether.  Picric  acid 
naturally  takes  the  form  of  pure  white  crystals  ;  but  when  these  are 
fused  and  cast  (a  rather  dangerous  operation),  it  resembles  beeswax. 
The  intensity  of  action  of  this  explosive  is  probably  much  exaggerated. 
The  French  Government  is  manufacturing  large  quantities.  Until  more 
is  known  about  it  the  actual  value  cannot  be  compared  with  that  of  other 
explosives.     Reports  are  conflicting  and  contradictory. 


Different  Explosives  Compared.  45 

Jioburite. — The  intensity  of  action  of  this  explosive  under  water  is 
not  known,  but  it  has  been  adopted  for  use  by  Mr.  Lay  in  his  loco- 
motive torpedo,  and  it  is  therefore  in  all  probaljility  a  powerful 
submarine  explosive. 

The  product  of  its  gas  volume  and  units  of  heat  =  1,150,000,  dyna- 
mite No.  1  being  950,000  {vide  Engineering,  page  532,  8th  November, 
1887).  From  this  it  would  appear  that  its  relative  power  is  121  to  100 
for  dynamite  and  to  142  for  blasting  gelatine. 

Experiments  at  Chatham  have  been  carried  out  by  the  Royal  Engi- 
neers, which  show  that  its  intensity  of  action  when  used  for  land 
purposes  is  distinctly  inferior  to  gun-cotton.  Carl  Roth's  specification, 
No.  9166,  July  14,  1886,  should  be  studied  in  connection  with  this  new 
German  explosive.  It  is  one  of  the  Sprengel  class,  like  rackarock,  but 
the  ingredients  are  each  solid.  The  patentee  claims  the  process  of  pro- 
ducing explosives  by  the  mixture  of  substances  rich  in  oxygen,  such  as 
potassium  nitrate,  with  a  compound  obtained  from  coal  tar  or  from 
fractional  products  of  the  .same,  by  incorporating  therewith  both 
chlorine  and  nitrogen.  Six  examples  are  given  for  producing  such  a 
compound,  one  of  the  most  successful  being  thus  made  :  12  1b.  of  nitric 
acid  (1.45  specific  gravity)  are  heated  with  4  lb.  sodium  chloride  for  one 
hour  to  60  deg.  Cent.,  and  then  cooled;  2  lb.  naphthaline  are  then  added 
in  small  portions  to  the  mixture,  and  towards  the  conclusion  of  the  re- 
action the  whole  is  gently  heated.  A  reddish  mass  separates  out,  and 
is  freed  from  salt  by  washing.  It  is  then  digested  for  several  hours 
with  a  mixture  of  three  parts  nitric  acid  (specific  gravity  1.52)  to  six 
parts  of  sulphuric  acid  (concentrated).  A  brownish  yellow  crystalline 
substance  is  produced,  which,  after  washing,  &c.,  has  a  specific  gravity 
of  1.4.  By  mixing  one  part  of  same  with  two  parts  of  potassium 
nitrate  a  very  powerful  explosive  is  obtained.  It  is  claimed  "  that  the 
chlorine  exerts  a  loosening  efiect  on  the  atomic  groups  containing  the 
nitrogen,  and  accordingly  enables  the  said  groups  to  react  more  readily 
on  the  oxygen  yielding  substances. " 

Roburite  cannot  be  exploded  by  a  blow  or  by  friction.  A  red-hot 
poker  can  be  put  into  a  mass  of  it  with  impunity,  and  if  placed  in  a 
smith's  fire  it  burns  slowly.  Its  explosion  when  effected  by  a  strong 
detonating  fuze  proves  it  to  be  a  powerful  detonating  mixture.  A  new 
departure  in  the  manufacture  of  detonating  explosives  has  been  arrived 
at,  but  roburite  does  not  appear  to  be  well  adapted  for  submarine 
mining,  as  its  power  is  affected  by  damp.  Its  power  can,  however,  be 
restored  by  drying. 

The  following  Table  gives  the  values  of  E  for  Abbot's  formula  for 
each  explosive  mentioned  : 


46 


Submarine  Minin 


Table  XVIII. 


Intensity  of 

Explosives. 

Action  under 
Water. 

Value  for  E. 

Dynamite 

100 

186* 

Gun-cotton            

87 

135*A 

100 

E 

Dualin        

111 

232 

Lithofracteur  or  rendrock 

94 

160 

Giant  powder       

83 

120 

Vulcan     ,,             

82 

114 

Mica         „             

83 

119 

Nitro-glyceriiie     

Hercules  powder 

81 

111 

106 

211 

Electric        ,,         

69 

67 

Designolle  .,         

68 

65 

Brugere  or  piciiu  powder 

80 

110 

Tonite         

85 

126 

Explosive  gelatiue,  1881 

117 

259* 

Blasting  gelatine,  1884   ... 

142 

375* 

Atlas  powder  (A) 

100 

186 

„      (B) 

99 

183 

Judson      „        (5) 

78 

100 

„     (3F) 

62 

45 

„     (CM) 

44 

Rackarock 

88 

140 

Forcite  gelatine    .. 

133 

333* 

Gelatine  dynamite  (No.  1) 

123 

254 

(No.  2) 

? 

? 

Gelignite 

102 

192 

Roburite 

' 

' 

Remarks.— (A)  Abbot.      (E)  English  experiments, 
are  specially  applicable  for  submarine  work. 


Those  marked  with 


Best  Explosives  for  Submarine  Mining. 

The  foregoing  descriptions  of  the  best-known  high  explosives  show 
tliat  dynamite,  gun-cotton,  gelatine  dynamite,  blasting  gelatine,  and 
forcite  gelatine  are  the  most  suitable  for  submarine  work.  These  explo- 
sives will  now  be  examined  in  detail. 

Dynamite. — I  =  100,  specific  gravity  =  1.6  ;  has  been  before  the  public 
so  many  years  and  is  so  well  known  that  it  is  not  necessary  to  describe 
it.  When  slowly  heated  to  420  deg.  Fahr.  it  is  liable  to  explode  with 
great  violence.  If  frozen  it  should  bo  thawed  in  a  vessel  jacketted  with 
water  at  a  temperature  not  exceeding  130  deg.  Fahr.  It  is  manufac- 
tured both  in  Europe  and  America,  and  is  sold  at  a  reasonable  price — 
about  Is.  5d.  a  pound.  It  is  powerful,  easily  detonated  (too  easily),  it 
only  loses  6  per  cent,  of  its  power  when  the  cliarge  is  drowned  by 
water,  but  General  Abbot  declares  that  the  water  does  not  cause  exuda- 
tion of  nitro-glycerine  if  tlie  charge  be  in  the  granular  form  and  not  in 
tlie  form   of  compacted  cartridges ;  it  can   be  detonated  wlien   in   the 


Dynamite. — Gun-Cotton.  47 

frozen  state  if  granular  and  not  in  cartridges  ;  it  remains  in  good  order 
after  long  storage,  but  it  freezes  at  40  deg.  Fahr.,  and  should  be  thawed 
before  it  is  used ;  it  is  quite  safe  when  handled  with  reasonable  care ; 
when  used  in  the  granulated  state  the  cases  can  be  loaded  through  a 
small  hole ;  it  does  not  vary  with  different  samples,  and  is  on  the  whole 
a  trustworthy  explosive.  When  using  dynamite  the  printed  instruc- 
tions and  cautions  should  be  carefully  followed.  Its  power  is  now, 
however,  outmatched  by  blasting  gelatine  and  forcite  gelatine  per  unit 
of  weight,  and  as  these  explosives  are  not  equally  open  to  the  objection 
of  producing  the  nitro-glycerine  headaches  to  those  who  manipulate 
them,  and  are  not  so  easily  detonated,  and  therefore  not  so  liable 
to  sympathetic  detonation,  or  to  accidental  explosion,  especially 
when  frozen,  they  are  considered  to  be  superior  in  many  important 
particulars  and  infei-ior  in  none.  Dynamite  was  chosen  for  the 
service  explosive  for  submarine  mining  in  the  United  States,  but 
it  is  now  understood  that  blasting  gelatine  may  take  its  place  for  that 
service. 

Gun-Cotton. — 1  =  100.  This  also  has  been  a  long  time  before  the 
public,  and  its  chief  characteristics  and  manufacture  are  well  known. 
It  was  discovered  by  the  German  Professor  Schonbein,  and  the 
Austrians  made  many  costly  experiments  with  a  view  to  introduce  it  as 
a  war  explosive.  It  was  manufactured  by  them  in  a  fibrous  form  and 
plaited  into  yarns,  but  the  chemical  and  mechanical  methods  pursued 
did  not  free  it  from  acid  impurities.  Such  gun-cotton  may  become 
dangerous  after  storage.  In  the  English  method  of  manufacture  the 
impurities  are  more  thoroughly  removed.  Invented  by  a  celebrated 
chemist  who  has  made  the  study  of  explosives  his  speciality,  and  who 
has  hcen  the  Government  adviser  for  a  great  number  of  years,  it  has 
been  developed  under  peculiar  advantages  and  has  been  employed  in 
the  numerous  experiments  due  to  the  evolution  of  torpedo  warfare 
in  this  country. 

The  great  safety  with  which  in  the  wet  state  it  can  be  stored  and 
manipulated,  and  the  important  fact  that  it  can  be  and  is  employed  in 
the  wet  state  as  an  explosive,  constitute  its  chief  merits.  The  fact  that 
wet  gun-cotton  can  be  detonated  was  one  of  several  important  dis- 
coveries made  by  one  of  Sir  Frederick  Abel's  assistant,  the  late  Mr.  E. 
O.  Brown.  Gun-cotton,  when  wet,  is  peculiarly  insensitive  to  detona- 
tion, and  consequently  to  sympathetic  explosion  when  neighbouring 
charges  are  fired.  This  insensitivity  is  a  great  safeguard  against 
acccidents  of  all  kinds.  When  wet  it  can,  like  wood,  be  sawn  or  cut 
into  any  desired  shape. 

Its  cliief  defect  at  the  present  date  is  want  of  strength  (when  used 


48  Submarine  Mining. 

under  water)  per  unit  of  weight  or  of  cost  as  compared  with  other  high 
explosives  invented  more  recently.  Also  it  is  somewhat  difficult  and 
costly  to  manufacture  in  a  pure  and  perfect  condition,  and  the  principal 
output  is  consequently  confined  to  the  Government  establishments  in 
those  countries  which  have  adopted  it  as  a  war  store  both  for  the  land 
and  sea  services.  Even  when  so  made  with  the  utmost  care,  its  continued 
maximum  efficiency  after  lengthened  storage  has  never  been  attained 
except  when  stored  dry.  For  this  reason,  and  because  it  is  generally 
stored  wet,  large  quantities  are  not  kept  in  reserve,  and  during  a  time 
of  war  it  is  therefore  improbable  that  a  sufficient  amount  could  be 
manufactured  to  meet  all  requirements.  When  stored  wet,  it  gradually 
becomes  spongy  fi-om  frequent  wetting.  This  can  be  obviated  by  storing 
it  between  end  plates  firmly  braced  together  by  screw  bolts  as  suggested 
by  the  author  in  January,  1875,  but  which  has  only  been  partially  and 
imperfectly  done  in  the  mines  of  the  Royal  Navy.  Sir  Frederick  Abel 
has  always  laid  great  stress  on  the  necessity  for  retaining  the  density 
of  the  gun-cotton  as  issued  from  the  manufactory,  but  General  Abbot's 
experiments  with  gun-cotton  appear  to  indicate  that  equal  effects  are 
produced  under  water  from  equal  weights,  whether  the  gun  cotton  be 
in  slabs  or  in  the  more  bulky  granulated  form. 

In  buoyant  mines  the  present  practice  is  to  employ  an  air  space 
round  the  charge,  and  it  would  therefore  appear  to  be  immaterial 
whether  the  gun-cotton  take  the  form  of  a  solid  mass  or  of  a  larger 
charge  of  the  gi'anulated  material,  so  long  as  equal  weights  are  inserted. 
The  amount  of  water  usually  added  to  dry  gun-cotton,  to  wet  it,  is 
25  per  cent.  Thus  a  charge  of  125  lb.  of  wet  gun-cotton  contains  100  lb. 
of  actual  gun-cotton. 

The  size  of  the  slabs  used  for  the  submarine  mining  service  in  Eng- 
land is  6i  in.  by  6^  in.  by  1|  in.,  and  each  weighs  about  2i  lb.  when 
dry,  the  compression  in  manufacture  being  perpendicular  to  the  larger 
surfaces,  and  the  cleavage  afterwards  being  parallel  thereto.  The  aboAc 
figures  show  that  a  cubic  foot  of  English  gun-cotton  weighs  about  G6  lb. 
dry  and  82i  lb.  wet. 

Gun-cotton  is  also  made  in  Russia  in  cylinders  15  in.  in  diameter  and 
Al  in.  high,  weighing,  when  dry,  25  lb.,  which  is  at  the  rate  of  54^  lb. 
per  cubic  foot.  The  French  gun-cotton  is  formed  into  slabs  4|  in.  x 
4|  in.  X  1.6  in.,  weighing  22  oz.,  which  gives  the  same  specific  gravity 
as  the  Englisii  gun-cotton. 

As  regards  the  relative  intensity  of  action  of  gun-cotton  when  deto- 
nated under  water,  it  appears  that  quick  detonation  in  the  open  air 
afibrds  no  reliable  measure  of  the  force  obtained  for  damaging  a  ship's 
bottom. 


Tonite. — Explosive  Gelatine.  49 

Sir  Frederick  Abel's  experiments  with  small  charges  in  air  against 
iron  plates  a  short  distance  off,  although  interesting,  do  not  appear  to 
lead  to  any  useful  data  for  submarine  work.  Also  his  experiments  with 
small  charges  in  bore-holes,  although  useful  for  rock  blasting,  are  not 
for  the  most  part  applicable  to  submarine  mining.  For  such  work  it  is 
absolutely  necessary  to  record,  collate,  and  examine  a  great  number  of 
carefully  conducted  trials  under  water. 

The  low  figure  of  efficiency  for  nitro-glycerine  when  used  under  water 
in  its  undiluted  state  forms  a  striking  example,  and  shows  how  mis- 
leading may  be  the  results  of  experiments  in  air  when  applied  to 
subaqueous  explosions. 

As  before  stated,  the  American  coefhcients  for  relative  intensity  of 
action  are  principally  based  on  a  few  experiments  with  small  charges 
of  each  explosive,  and  the  coefficient  for  gun-cotton,  viz.,  87  per  cent,  of 
that  for  dynamite,  differs  considerably  from  that  which  was  obtained 
by  experiments  in  England,  where  it  was  shown  to  be  rather  superior 
to  No.  1  dynamite.  Either  the  gun-cotton  used  in  America  was  of 
inferior  quality,  or  the  dynamite  used  in  England  was  inferior  to  that 
tried  at  Willet's  Point. 

Tonite. — 1  =  85.  Composition  =  52.5  per  cent,  gun-cotton,  47.5  per 
cent,  of  barium  nitrate.  Specific  gravity  =  1.28.  This  explosive  is 
made  at  Faversham,  in  England,  by  the  Cotton  Powder  Company, 
and  also  in  California,  U.S.,  under  assigned  patents.  The  English 
railroads  carry  tonite  on  the  same  conditions  as  gunpowder,  but 
refuse  to  carry  dynamite  or  compressed  gun-cotton.  Dry  tonite  is 
made  up  into  candle-shaped  cartridges  covered  with  paper  and  water- 
proofed, usually  with  paraffin.  Some  of  these  cartridges  are  perforated 
to  take  a  detonator,  and  are  then  called  primers. 

Wet  tonite  contains  about  18  per  cent,  of  added  water,  i.e.,  118  lb. 
of  wet  tonite  contains  100  lb.  of  tonite.  It  is  granular,  uncompressed, 
and  is  taken  from  the  incorporating  mill  before  going  to  the  press- 
room. 

The  experiments  at  Willet's  Point  indicate  that  equal  amounts  of 
tonite,  whether  dry  in  compacted  cartridges,  or  wet  in  the  uncom- 
pressed granular  form,  pi'oduce  equal  effects  by  submai-ine  explosion. 

Explosive  Gelatine,  1881. — 1  =  117,  specific  gravity  =  1.54.  Com- 
position =  89  per  cent,  nitro-glycerine ;  7  per  cent,  nitro-cotton  ;  4  per 
cent,  camphor.  In  1867,  Professor  Abel  combined  nitro-glycerine  and 
gun-cotton  to  form  what  he  termed  glyoxilin.  He  used  tri-nitro  cellulose. 
The  explosive  was  practically  a  mechanical  mixture.  The  percentage  of 
nitro-glycerine  was  considerably  less  than  in  dynamite.  Nobel  after- 
wards found  that  when  a  lower  pi-oduct  of  the  nitration  of  gun-cotton,  \iz., 


50  Submarine  Mining. 

collodion  or  soluble  gun-cotton  (Abbot  calls  it  nitro-cotton),  be  used  in 
certain  proportion  in  place  of  tri-nitro  cellulose,  there  is  a  change,  and  the 
result  has  "  almost  the  character  of  a  compound  "  (Abel).  By  macerating 
from  10  to  7  per  cent,  of  soluble  gun-cotton  with  90  to  93  per  cent,  of 
nitro-glycerine,  a  yellow,  plastic,  gummy  jelly  results,  from  which 
neither  nitro-glycerine  nor  gun-cotton  can  be  easily  separated. 

The  addition  of  4  per  cent,  of  camphor  makes  explosive  gelatine  very 
insensitive  to  detonation  from  shock  so  long  as  it  remains  unfrozen.  A 
rifle  bullet  at  100  yards'  range  striking  a  naked  slab  3  in.  thick,  and 
flattening  itself  on  an  iron  plate  against  which  the  slab  rests,  has  failed 
to  ignite  the  explosive. 

Lengthened  submersion  in  water  causes  little  or  no  exudation  of 
nitro-glycerine.  It  flames  when  ignited  like  dry  gun-cotton  or  dyna- 
mite. It  becomes  soft  and  somewhat  greasy  at  140  deg.  Fahr.,  and 
it  freezes  at  about  40  deg.  Fahr.  It  can  be  cut  with  a  knife.  Its 
specific  gravity  is  1.54.  The  presence  of  the  camphor  pi-e vents  it  from 
detonating,  as  it  otherwise  does  when  heated  slowly  to  400  deg.  Fahr. 
When  camphorated  it  burns  with  sparks  at  about  570  deg.  Fahr. 
To  insure  its  detonation  the  Aystrians  employ  a  special  primer 
made  of  60  per  cent,  nitro-glycerine  and  40  per  cent,  nitro-hydro- 
cellulose  (Jekyll.  Royal  Engineer  Corps  papers).  The  latter  is  formed 
by  first  treating  cotton  with  sulphuric  and  afterwards  with  nitric  acid. 
When  mixed  with  the  nitro-glycerine,  a  white  soapy  substance  is 
formed,  20  grammes  of  which  sufiice  to  detonate  a  charge  of  explosive 
gelatine  with  certainty.  The  intensity  of  action  1=117  was  obtained 
from  the  American  experiments  in  1881,  in  which  the  explosive  was  of 
inferior  (juality,  subsequent  long  storage  of  a  portion  of  it  proving  that 
the  nitro-cotton  was  impure.  Moreover,  the  gun-cotton  or  dynamite 
priming  charges  employed  sometimes  [failed  altogether  to  detonate  the 
charges  of  gelatine,  which  must  have  been  bad. 

Blasting  Gelatine,  1884. — 1  =  142.  Composition  =  92  per  cent, 
nitro-glycerine  and  8  per  cent,  collodion  gun-cotton,  specific  gravity  = 
1.53  to  1.55.  The  sample  (2000  1b.)  for  Abbot's  experiments  was 
supplied,  as  to  the  trade,  from  Scotland  without  any  added  camphor. 
The  makeis,  Nobel's  Explosive  Company,  state  that  it  can  be  added  if 
desired,  as  follows :  "  Warm  gently  by  means  of  water  at  60  deg. 
Cent.,  and  when  the  gelatine  attains  a  soft  plastic  state,  with  a  tem- 
perature of  40  deg.  Cent,  in  the  mass,  5  per  cent,  of  camphor  dissolved 
in  alcohol  may  be  added  and  completely  incorporated  with  the  hand  to 
form  a  homogeneous  mass.  The  warming  is  best  done  in  a  copper 
basin  surrounded  with  water  at  60  deg.  Cent.  ;  40  lb.  or  50  lb.  may  be 
camphoratod  at  a  time!  in  the  above  manner." 


Blasting  Gelatine. — Forcite.  51 

The  experiments  made  by  (Jeneral  Abbot,  from  whose  records  the 
above  value  of  I  is  taken,  were  carried  out  with  tlie  uiicamphorated 
gelatine,  and  most  of  the  cliarges  were  detonated  with  a  service 
(American)  fuze,  viz.,  a  copper  capsule  containing  24  grains  of  fulmi- 
nating mercury.  Several  shots  were  also  lired  with  a  3-oz.  tonite 
primer,  and  the  results  proved  that  full  effects  were  produced  with 
the  fuze  alone. 

Experiments  were  made  to  test  it  for  sympathetic  explosion,  the 
gelatine  being  placed  in  thin  rubber  bags  at  various  distances  from  a 
primary  charge  of  1  lb.  of  dynamite.  At  5  ft.  explosion  occurred,  but 
at  5  ft.  9  in.  and  over  no  explosion  occurred.  It  would  have  been 
more  satisfactory  if  the  primary  charge  had  been  1  lb.  of  the  gelatine. 
Naked  charges  hung  against  wooden  boards  were  fired  at  by  a  rifle  at 
a  range  of  twenty  paces.  Tlie  gelatine  blazed  when  struck,  and  on 
one  occasion  a  small  explosion  occurred,  throwing  unignited  fragments 
of  the  cartridges  a  few  feet  from  the  target.  When  lighted  with  a 
match  it  burns  with  an  intense  wliite  flame. 

"  Blasting  gelatine  without  camphor  is  most  admirably  suited  to 
submarine  mining,  in  so  far  as  strength  and  ordinary  physical 
properties  are  concerned.  For  military  purposes  on  land  a  small 
percentage  of  camphor  should  not  be  omitted."     (Abbot.) 

This  explosive,  whether  camphorated  or  not,  may  be  kept  im- 
mersed in  water  for  a  length  of  time  without  undergoing  any  important 
change.  "  It  has  consequently  been  proposed  to  render  the  storage 
of  blasting  gelatine  and  certain  of  its  preparations  comparatively  safe 
by  keeping  them  immersed  in  water  till  required  for  use."  (Abel.) 
This  is  rather  hard  on  blasting  gelatine,  for  it  implies  that  tliis  pre- 
caution is  necessary  in  order  to  make  its  storage  only  "  comparatively 
safe."  So  far  as  present  knowledge  goes,  this  explosive  can  be 
stored  dry  as  safely  as  gunpowder,  "cool  and  dark  storage"  being 
secured  whenever  possible.  (Abbot.)  The  deterioration  in  store 
which  occurred  in  the  early  samples  sent  to  America,  were  apparently 
due  to  impurities  in  the  nitro-cotton,  but  this  is  now  provided  against 
by  great  care  in  tlie  manufacture.  Nevertheless,  the  difliculty  of  pro- 
ducing pure  nitro-cotton  is  well  known,  and  this  leads  us  to  forcite, 
in  which  it  is  avoided. 

Forcite  (No.  1  extra). — 1  =  133.  Composition  =  95  per  cent,  nitro- 
glycerine, and  5  per  cent,  cellulose. 

Forcite  (No.  1).  —I  =  124.  Composition  =  75  per  cent,  nitro-glycerine, 
7  per  cent,  cellulose,  and  18  per  cent,  nitre. 

Forcite  Q^o.  2). — 1  =  95.     Composition  =  40  per  cent,  nitro-glycerine 
and  60  per  cent,  explosive  base  (nature  unknown). 
e2 


52  Sii^bmarine  Mlnliuj. 

Forcite  (No.  3  0). — I  =  88.  Composition  =  30  per  cent,  nitro-glycerine 
and  70  per  cent,  explosive  base  (nature  unknown). 

Specific  gravity,  No.  1  extra  =  1.51,  No.  1  =  1.6,  No.  3  =  1.66,  No.  3  C 
=  1.69. 

Tliey  can  all  be  detonated  witli  a  fuze  containing  24  grains  of  ful- 
minating mercury.  No  increased  power  was  obtained  when  a  larger 
priming  charge  =  3  oz.  of  tonite  was  employed.  Tlie  explosive  base 
employed  in  the  lower  grades  is  probably  some  combination  of  sodium 
nitrate  witli  resin,  coal  dust,  &c.,  mixed  with  cellulose  and  sometimes 
with  dextrine.  As  regards  sympathetic  explosion,  the  highest  grade 
acts  similarly  to  explosive  gelatine,  exploding  at  5  ft.  from  a  primary 
charge  of  1  lb.  of  dynamite  under  water.  It  will  be  remembered  that 
dynamite  itself  explodes  at  20  ft.  under  like  conditions.  "No.  1  extra" 
forcite — or  forcite  gelatine — contains  no  gun-cotton  or  nitro-cotton,  but 
simply  unnitrated  cellulose,  combined  with  nitro-glycerine.  Cotton  is 
treated  alternately  with  acids  and  alkalies,  as  for  paper  stock,  leaving 
pure  cellulose  which  is  reduced  to  a  powder  and  then  exposed  to  high- 
pressure  steam  in  a  closed  vessel  until  it  becomes  a  gelatinous  mass. 
This  can  be  stored  for  any  length  of  time  in  Avater  ;  95  per  cent,  of 
nitro-glycerine  can  be  incorporated  with  it  to  form  a  highly  explosive 
jelly,  very  similar  to  explosive  gelatine,  both  in  its  appearance  and 
properties.  It  is  claimed,  and  apparently  with  justice,  that  its  manu- 
facture is  less  costly  than  similar  compositions  of  nitro-glycerine.  Also 
that  tlie  nitro-glycerine  is  so  completely  incorporated  that  it  cannot  be 
separated  even  by  the  application  of  alcohol  or  sulphuric  ether.  Also 
that  water  has  no  action  upon  it,  that  it  detonates  with  the  greatest 
violence,  that  it  burns  away  harmlessly  in  the  open  air.  General  Abbot 
concludes  the  report  on  a  careful  series  of  small  charge  experiments  with 
forcite  as  follows  :  "  These  investigations  indicate  that  forcite  must  be 
classed  as  one  of  the  explosives  worthy  of  serious  consideration  when  it 
becomes  necessary  to  defend  our  coasts  with  submarine  mines.  Its  great 
strength  is  fully  established  ;  its  permanency  for  long  periods  of  time 
remains  to  be  studied." 

Inasmuch  as  pure  cellulose  is  easier  to  manufacture  than  pure  nitro- 
cellulose, it  would  appear  that  its  permanency  can  be  more  easily  assured 
than  tliat  of  explosive  or  blasting  gelatine.  As  regards  their  comparative 
intensities  of  action,  the  difference  is  in  favour  of  Nobel's  explosive. 
Forcite  is  the  invention  of  a  French  chemist,  M.  John  M.  Lewin,  who 
patented  it  in  Belgium  in  November,  1880,  but  it  is  evidently  a  very 
close  copy  of  blasting  gelatine. 

Gelatine  Di/namile  (No.  1). — 1  =  123,  specific  gravity  =  1.55.  (No.  2) 
I^not  known.     Composition  (No.  1)  =  65  per  cent.  A  and  35  per  cent. 


Gelatine  Dyvamife. — CovcJusions.  53 

B.  Composition  (No.  2)  =  45  per  cent.  A  and  55  per  cent.  B.  A  =  97.5 
per  cent,  nitro-glycerine  and  2.5  per  cent,  soluble  gun-cotton,  B  =  75  per 
cent,  potassium  nitrate,  24  per  cent,  cellulose,  1  per  cent.  soda.  These 
lower  grades  of  explosive  gelatine  are  manufactured  and  sold  to  compete 
with  the  various  explosives  in  the  market  for  blasting  pui'poses.  They 
have  not  been  tried  by  General  Abbot,  and  the  value  of  I  given  was 
found  as  follows  :  The  makers  (Nobel's  Explosive  Company)  state  that 
its  relative  intensity  of  action  is  132,  but  they  also  give  blasting  gelatine 
at  153.  For  submarine  work  blasting  gelatine  should  be  142  according 
to  Abbot,  and  reducing  132  in  the  same  proportion,  123  is  obtained. 

Tlie  makers  of  the  gelatine  dynamites  state  that  they  are  much  more 
powerful  than  dynamite,  more  convenient  to  handle,  and  more  economical, 
i.e.,  a  greater  effect  per  unit  of  cost.  The  latter  is  open  to  doubt  (see 
Table,  page  54).  Moreover,  they  are  unaffected  by  water,  and  are  less 
sensitive  to  detonation,  and  therefore  to  accidental  explosion  by  a  blow. 
They  require  to  be  detonated  by  special  gelatine  detonators  supplied  by 
the  manufacturers.  They  freeze  at  40  deg.  Fahr.  When  frozen  they 
should  be  carefully  thawed  by  means  of  a  water  bath  (water  not  over 
130  deg.  Fahr.)  in  accordance  with  the  printed  directions  issued  with 
them.     They  should  never  be  exposed  to  a  tropical  sun. 

Gelatine  dynamite  (No.  1)  appears  to  be  well  adapted  for  submarine 
work. 

Generally,  all  the  nitro-glycerine  compounds  should  not  be  kept  for 
long  periods  at  a  higher  temperature  than  130  deg.  Fahr.  They  can  be 
tested  in  small  quantities  to  160  deg.  Fahr.,  but  any  temperature  over 
140  deg.  Fahr.  is  dangerous. 

In  conclusion,  the  efficiency  of  an  explosive  for  submarine  mining 
depends  not  only  upon  the  intensity  of  action  per  unit  of  weight,  but 
upon  the  intensity  of  action  per  unit  of  cost,  and  also  per  unit  of  space 
occupied. 

The  approximate  cost  and  weight  of  each  of  the  best  explosives  for 
submarine  mining,  as  well  as  their  relative  intensities  of  action  per  unit 
of  weight,  cost,  and  space,  are  given  in  Table  on  next  page.  It  will 
be  seen  that  blasting  gelatine  heads  the  list  in  every  case,  although 
lower  values  are  given  to  it  than  the  manufacturers  claim  as  its  due. 
For  ground  mines  gelatine  dynamite  and  dynamite  are  nearly  as 
economical  as  blasting  gelatine,  but  they  require  larger  and  therefore 
more  expensive  mine  cases. 

For  buoyant  mines  blasting  gelatine  is  the  best  explosive. 

When  the  high  explosives  cannot  be  obtained  in  sufficient  quantities 
at  a  time  of  emergency,  gunpowder  can  be  used  effectively,  especially 
in  the  ground  mines  :  a  line  is   therefore  added  to  the  Table  for  gun- 


54 


Submarine  Mining. 


powder.  When  used  every  care  must  be  taken  to  place  it  in  strong 
cases,  and  to  ignite  it  by  means  of  lightning  fuze  coiled  near  the  outside 
of  the  charge  This  causes  the  outside  of  the  charge  to  be  ignited  first, 
forming  an  outer  surface  of  gas  at  a  high  temperature,  and  protecting 
that  portion  of  the  charge  which  is  ignited  last  from  being  drowned 
when  the  case  is  ruptured.  In  this  manner  it  is  probable  that  the 
whole  of  the  gunpowder  charge  would  be  ignited  and  burnt.  Such  an 
arrangement  is  especially  necessary  when  gunpowder  mines  ai-e  im- 
provised with  weak  cases  like  barrels.  It  should  be  noted  that  owing 
to  its  low  price,  the  efficiency  of  gunpowder  per  unit  of  cost  is  more  than 
three  times  its  efficiency  per  unit  of  weight,  but  the  figure  85  somewhat 
overstates  the  matter,  because  a  larger  and  therefore  a  more  expensive 
mine  case  is  required  when  gunpowder  is  used  for  submarine  work. 

Experiments  of  late  years  have  been  conducted  almost  entirely  with 
gun-cotton  in  England  and  dynamite  abroad.  Gunpowder  has  been 
neglected.  It  is  very  desirable  that  some  large  ground  charge  ex- 
periments should  be  conducted  with  this  useful  and  well-known 
explosive,  and  perhaps  with  some  of  the  other  forms  of  cheap  ex- 
plosive mixtures,  especially  Judson's  powder. 


Table  XIX. 


-Relative  Values  of  Explosives  for 
Submarine  Mining. 


■2   . 

a 

Efficiency  under  Water. 

>> 

sf 

■o 

^ 

^ 

a 

Description  of  Ex- 
plosive. 

o(2 

.3 

oi 

i 

S 

Remarks. 

1 

i 

P 

11 

5  § 

1 

Blasting  gelatine 

1.54 

96.3     24 

142 

138 

101 

Forcite  gelatine  . . . 

1.51 

95.4      ? 

133 

127 

turing        cost 
cannot        be 
greater      than 
that   of  blast- 
ing    gelatine, 
and     is     pro- 
bably less. 

.s 

Gelatine  dynamite 

1.55 

96.9  '  21 

123 

119 

99 

4 

Dynamite,   No.    1. 

1.6 

100 

17 

100 

100 

100 

={ 

Gun-cotton,  dry... 

l.Ofi 

66 

27 

100 

66 

63 

(iun-cotton,  wet... 

1.32 

82,5 

80 

66 

63 

25  per  cent,  of 

added  water. 

fi 

Tonite       

l.'iS 

80 

85 

68 

7 

Gunpowder 

0.9 

56 

5 

25 

14 

85 

55 


CHAPTER  V. 

Considerations  Guiding  the  Size  and  Nature  of  Mine  Cases,  &c. 

All  submarine  mines  can  be  classified  as  follows.  Class  A  :  Mines 
that  are  caused  to  explode  when  in  contact  with,  or  very  close  to  a 
vessel's  side  or  bottom.     Class  B  :  Mines  that  act  at  a  greater  distance. 

All  submarine  mines  can  also  be  placed  in  two  divisions.  Division  1 : 
Mines  under  control ;  these  are  electrical.  Division  2  :  Mines  not 
under  control,  whether  they  be  electrical,  mechanical,  chemical,  or  some 
combination  of  these  three. 

Concerning  Class  A,  it  has  already  been  calculated  that  3.3  lb.  of 
gun-cotton  or  dynamite  properly  placed  form  an  ample  charge  to 
fatally  injure  a  modern  man-of-war,  and  this  agrees  witli  the  ex- 
periments against  the  Oberon,  which  show  that  33  lb.  of  gun-cotton 
contained  in  a  case  without  any  air  space,  and  not  enveloped  witli 
a  wooden  jacket,  will  break  through  tlie  double  skin  of  H.M.S. 
Hercules  when  exploded  4  ft.  off  it.* 

7Vte  Enij^loyment  of  Wooden  Jackets  not  Desirable. — Tlie  great  loss  of 
power  produced  by  surrounding  the  mine  case  with  a  slieathing  of  wood, 
or  other  similar  material  sucli  as  cork,  has  already  been  noted.  Tlie 
employment  of  wooden  or  cork  jackets  to  give  buoyancy  to  mines  cannot 
therefore  be  entertained  for  a  moment. 

Loss^^  of  Effect  due  to  an  Air  Space  in  a  Mine. — An  equal  loss  of 
power  is  not,  however,  produced  by  employing  an  air  space  in  a  mine 
to  give  the  required  buoyancy.  Experiments  made  in  America  to  test 
the  effect  of  such  air  space  show  that  a  certain  loss  of  power  is  occasioned. 
Unfortunately  the  charges  employed  did  not  exceed  8  lb.  of  dynamite, 
and  the  cases  were  simply  tin  cylinders.  These  experiments  demonstrated 
that  with  an  air  space  not  exceeding  three  times  the  volume  of  the  charge 
no  sensible  effect  on  the  intensity  of  action  was  observed  ;  but  when  the 
air  space  was  increased  to  five  times  the  volume  of  the  charge  of  dynamite, 
the  mean  pressure  recorded  fell  from  8.554  to  6038,  a  loss  of  nearly 
30  per  cent,  in  tlie  intensity  of  action  as  recorded  in  crusher  gauges 
placed  8  ft.  from  tlie  centre  of  each  charge. 

*  See  foot-note  page  59. 


50  Sithmarine  Mining. 

General  Abbot  remarks  on  the  results  :  "Tlie  safe  limit  of  void  space 
for  small  charges  fired  under  water  lies,  therefore,  between  three  and 
live  times  that  of  the  charge." 

"  It  would  appear  altogether  probable  that  as  the  size  of  the  charge 
is  increased,  this  limit  increases  also,  and  hence,  that  the  void  space 
necessary  to  give  the  requisite  flotation  to  buoyant  torpedoes  does  not 
lessen  their  destructive  power.  For  ordinary  mines  of  this  character 
the  void  space  is  usually  between  two  and  three  times  that  occupied  by 
the  charge." 

"Whatever  may  be  the  practice  in  America,  such  a  small  air  space  is 
inadequate  when  the  cases  are  made  of  sufiicient  thickness  to  resist 
countermines,  and  of  sufficient  size  to  counteract  by  their  buoyancy  the 
sinking  action  produced  by  the  side  pressure  of  a  strong  tidal  current 
acting  on  a  mine  secured  to  the  bottom  by  a  single  mooring,  as  is  usual 
in  England.  It  is  therefore  to  be  regretted  that  no  experiments  have 
been  made  in  England  or  elsewhere  to  test  the  effect  of  employing  an 
air  space,  such  as  that  employed  in  our  service,  and  which  is  nearly 
twelve  times  the  volume  of  the  charge.  It  is  possible  that  so  large  an 
air  space  may  act  very  prejudicially,  and  warrant  a  different  arrange- 
ment of  charge,  mine  case,  &c. 

The  Evih  of  Using  Larger  Charges  than  are  Ahsohitely  Necessary. 
— In  all  demolitions  an  engineer  should  endeavour  to  use  charges,  each 
of  which  is  a  thoroughly  effective  minimum,  and  this  is  especially  neces- 
sary in  buoyant  submarine  mines.  Unnecessarily  large  charges  in 
contact  mines  produce  many  evils,  which  act  and  react  in  a  somewhat 
peculiar  manner. 

1.  A  large  charge  requires  a  large  case  to  buoy  it  up  even  in  dead 
water. 

2.  The  large  case  opposes  a  greater  resistance  to  tidal  or  other 
currents,  and  has  to  be  still  further  increased  when  moored  in  such 
currents. 

3.  The  large  case  must  be  made  of  thicker  metal  if  intended  to  be 
of  equal  efficiency  with  the  small  case  to  resist  the  effects  of  neigh- 
bouring explosions. 

4.  These  neighbouring  explosions  being  produced  by  mines,  like  itself, 
which  are  unduly  powerful,  it  must  be  made  of  still  thicker  metal  in 
order  to  be  safe  from  them. 

5.  This  again  requires  the  case  to  be  still  larger  in  order  to  buoy  up 
the  thicker  metal. 

6.  If  the  mines  be  spaced  further  apart  to  obviate  this,  it  does  not 
provide  a  strong  case  to  resist  countermining  by  a  foe. 

7.  There  is  a  waste  of  money  in  explosives. 


Electro-Contact  Mines.  57 

8.  The  mooring  gear  must  be  heavier  than  necessary. 

9.  The  periods  of  time  required  to  load  and  connect  up  the  mines, 
and  lay  them  and  pick  them  up  for  repair,  must  all  be  longer  than 
necessary,  and  this  alone  is  a  most  important  consideration  even  to  a 
country  that  can  afford  to  use  the  larger  and  more  costly  mines  on  the 
score  (whether  true  or  not)  of  increased  efficiency. 

Other  considerations,  all  pointing  in  the  same  direction,  could  be 
mentioned,  but  enough  has  perhaps  been  said  to  show  that  the  best 
contact  mine  is  one  that  contains  a  thoroughly  effective,  but  a  minimum 
charge. 

Existing  Custom. — It  is  and  always  has  been  usual  to  place  the 
apparatus  for  firing  and  testing  an  electro-contact  mine,  and  the  air 
space  for  buoying  it,  and  the  charge,  in  one  case.  It  is  perhaps  better  not 
to  do  so.  By  arranging  the  charge  in  a  small  case  that  will  just  contain 
it,  the  full  force  of  the  blow,  uncushioned  by  any  air  space  or  wooden 
jacket,  is  transmitted  direct  to  the  vessel's  side.  The  buoy  can  be  placed 
over  the  mine  and  separated  from  it  by  a  distance  apportioned  according 
to  the  charge  employed.  When  a  charge  of  100  lb.  of  gun-cotton  or 
dynamite,  or  anything  approaching  it,  is  used,  the  mine  should  be  8  ft. 
under  the  top  of  the  buoy,  and  the  electrical  apparatus  be  placed  in 
the  latter.  The  actual  distance  of  the  exploding  charge  from  the 
vessel  will  then  be  either  something  less  than  8  ft.  under  her  bottom,  or 
the  charge  will  be  close  to  the  ship's  side,  if  not  in  actual  contact  with 
it.  The  term  "contact  mine"  for  such  an  arrangement  may  appear 
to  be  a  misnomer,  but  it  is  a  convenient  one. 

A  comparison  of  the  results  of  the  Oberon  experiments  with  those 
recently  carried  out  at  Portsmouth  against  H.M.S.  Resistance,  as 
recorded  in  the  Times,  appear  to  indicate  that  small  charges  act  with 
greater  effect  when  not  in  actual  contact  with  a  vessel's  side,  but 
slightly  removed  from  it.  There  is  then  also  a  greater  chance  of 
making  large  holes  through  both  skins  of  the  double  bottom,  and  a 
greater  probability  of  drowning  more  than  one  compartment  of  the 
vessel,  and  of  placing  her  out  of  action.  If  then  a  charge  as  large  as 
100  lb.  be  used,  the  above  seems  to  be  the  most  reasonable  and  effective 
arrangement. 

For  reasons  already  given,  the  employment  of  a  smaller  charge  is 
advocated,  and  it  then  becomes  necessary  to  bring  it  closer  to  the 
vessel.  This  can  be  done  by  suspending  it  about  4  ft.  below  the  top  of 
the  buoy.  Fig,  21  shows  the  usual  arrangement  now  in  vogue.  Fig.  22 
shows  the  modification  now  recommended  if  the  large  100  lb.  charge  be 
retained.  Fig.  23  shows  the  plan  recommended  when  a  smaller  but 
sufficient  charge  is  used.     Fig.  24  shows  the  same  arrangement  in  the 


58 


Submarine  Mining. 


rare  event  of  tlie  top  of  the  buoy  first  bumping  the  bottom  of  a  vessel. 
This  special  occurrence  places  an  air  space  laetween  the  mine  and  the 
vessel's  bottom,  but  it  is  a  very  different  circumstance  to  that  illustrated 
in  Fig.  21,  where  the  charge  is  surrounded  by  an  air  space.  In  Fig.  24 
tlie  water  between  the  charge  and  the  buoy  is  driven  through  the  air 
space  and  strikes  the  vessel's  bottom  with  an  enormous  velocity,  which 
must  produce  nearly  as  destructive  an  effect  as  that  caused  by  an  ex- 
plosion, as  shown  in  Fig.  23,  and  wliicli  we  know  by  trial  to  produce 
the  desired  effect. 


Calculatioyi  for  the  Size  of  a  Mine  Case,  &c. — The  size  of  the  case 
for  a  contact  mine  being  limited  to  that  which  will  just  contain  the 
required  charge,  it  is  only  necessary  to  settle  upon  the  explosive  to  be 
employed  in  order  to  calculate  the  dimensions  of  the  case. 

Assume  that  blasting  gelatine  is  used.  Then,  as  23.5  lb.  will  destroy 
the  double  skin  of  a  modern  man-of-war  at  5  ft.,  let  50  per  cent,  be 
added  as  a  factor  of  safety,  and  we  arrive  at  a  charge  of  35.2  lb. 
Again,  as  96.3  lb.  of  this  explosive  can  be  placed  in  a  cubic  foot  of 
space,  the  content  of  a  mine  case  for  the  above  charge  =  f  cubic  foot. 

It  would  be  unnecessary  to  manufacture  a  spherical  case  of  such 
small  dimensions  (viz.,  1  ft.  diameter  and  less  than  ^  in.  skin),  as  a 
cylinder  only  9  in.  long,  and  the  same  internal  diameter,  with  ends 
dished  outwards,  is  large  enough,  and  if  made  of  J-in.  iron  would  resist 
a  sustained  collapsing  pressure  of  1894  lb.  per  scjuarc  inch  of  surface. 

Thus  (by  Rankine), 


),(i72,000r^ 
LxD      '- 


when   L  =  D  =  9   in.   and   t  =-  J. 


the 


Electro-Contact  Mines.  59 

strength  of  a  3-ft.  sphere  made  of  \-\n.  steel  being  P  =  9.'53  x  1.5  ;  say 
1400  lb.  on  square  inch.* 

The  weight  of  this  small  mine  case  is  a  little  under  15  lb.,  and  as  the 
weight  of  salt  water  displaced  by  it  is  24  lb.,  the  weight  of  the  case  in 
salt  water  when  it  is  loaded  with  blasting  gelatine  will  be  15  +  36 
—  24  =  27  lb.  A  good  and  trustworthy  electrical  apparatus,  complete 
with  its  metal  envelope  and  mouthpiece  (these  parts  will  be  described 
hereafter),  can  be  manufactured  so  as  to  weigh  not  more  than  25  lb.  to 
30  lb.  Thus  the  deadweight  of  the  suspended  charge  in  its  case  and 
of  the  electrical  apparatus  together,  need  not  be  more  than  50  lb.  or 
60  lb.  This  compares  with  a  weight  of  nearly  200  lb.  in  the  contact 
mines  now  made  for  the  English  service,  and  a  proportionately  smaller 
buoyant  body  can  therefore  be  employed.  This  buoyant  body  may 
consist  of  a  wooden  buoy  if  economy  be  aimed  at,  care  being  taken  to 
provide  against  water-logging  ;  or  it  may  consist  of  a  cork  buoy  covered 
with  a  waterproof  material,  or  it  may  be  a  steel  or  iron  case. 

If  wood  be  used,  the  body  should  not  possess  any  internal  air  space, 
because  it  would  then  be  easily  damaged  by  the  explosion  of  neigh- 
bouring mines  or  by  the  explosion  of  countermines.  It  should  be  solid, 
the  buoyancy  being  derived  from  the  mass  of  wood  used,  and  a  con- 
siderable excess  of  buoyancy  should  be  provided  to  meet  the  large  loss 
that  occurs  through  water-logging.  Experience  shows  that  the  diffi- 
culties thereby  engendered  are  well-nigh  insuperable,  and  the  same 
remark  applies  to  cork,  and  probably  to  all  substances  of  a  similar 
nature. 

When  a  wooden  or  cork  buoy  occupies  the  position  shown  in  Fig.  24 
(see  preceding  page)  it  does  not  act  prejudicially,  as  when  the  charge  is 
wooden  jacketted.  The  intervening  water  causes  the  buoy  to  act  as  a 
projectile,  and  the  result  is  probably  more  destructive  than  would  be 
obtained  with  an  air-spaced  buoy  similarly  situated.  The  latter  is, 
however,  to  be  preferred  for  reasons  already  given.  A  buoyant  body 
made  of  iron,  or  still  better  of  steel,  is  therefore  recommended.  The 
shape,  size,  and  thicknesses  have  next  to  be  considered. 

Considerations  Ruling  the  Size,  d'c,  of  a  Case  for  the  C iron  it-Closer 
(or  for  a7i  Electro-Contact  Mine). — What  are  the  requirements  1  The 
required  maxima  are:    1.   Buoyancy.     2.   Strength   to  resist   counter- 

♦  Since  writing  the  above,  it  has  been  pointed  out  to  the  author  that  ironclads 
and  other  war  vessels  are  now  built  with  two  strong  longitudinal  bulkheads, 
forming  coal  bunkers,  and  that  contact  mines  to  act  eifectively  against  such 
vessels  should  be  quite  twice  as  powerful  as  those  which  acted  effectively  against 
the  Oberon.  The  charge  for  an  electro-contact  mine  should  therefore  be  fixed  at 
72  lb.  of  blasting  gelatine,  instead  of  ^Ci  lb.,  as  stated  in  the  text. 


60 


Submarine  Mining. 


mines  and  rough  handling.     The  required  minima  are  :  1.  Weight.     2. 
Resistance  to  moving  water. 

As  regards  shape  the  above  maxima  and  minima  are  provided  for 
best  by  the  .sphere.  Buoyancy  and  weiglit  being  antagonistic,  it  is 
necessary  to  arrive  at  some  decision  concerning  the  strength  whicli  is 
required  in  practice.  It  may  be  accepted  that  a  spherical  case  3  ft.  in 
diameter,  made  of  ^-in.  steel,  is  strong  enough,  and  as  the  strength  to 
resist  a  collapsing  pressure  varies  inversely  with  the  square  of  the  dia- 
meter, and  directly  as  the  square  of  the  thickness,  we  can  at  once  find 
the  thickness  of  other  spherical  cases  of  the  same  material  whicli  shall 
possess  equal  strength.     Thus,  if 

s  =  strength  required, 

<  =  thickness  of  steel  in  inches, 

f?  =  diameter  of  sphere  in  inches. 
Then,  as 

S  oc    jr,  and  is  sufficient  when 


f 

=  Jan 

Ad 

r- 

(if 

.  t 

d 

144" 

The  following  Table  shows  the  thickness  of  steel  required  for  spherical 
cases  or  buoys  of  various  dimensions,  but  of  equal  strength,  to  a  3-ft. 
case  or  buoy  of  ^-in.  steel : 

Table  XX. 


Diameter  of 

Area  of  Dia- 

Tliickness of 

Weiprht  of 

Weight  Salt 

Buoyancy 

Sphere. 

metric  Plane. 

Steelin24thsin. 

Shell. 

Water  Displaced 

Empty. 

ft. 

sq.  ft. 

in. 

lb. 

lb. 

lb. 

1 

0.78 

2 

11 

32 

21 

1.5 

1.76 

3 

34 

115 

81 

2 

3.14 

4 

84 

269 

185 

2.5 

4.9 

5 

160 

525 

365 

3 

7.06 

6 

283 

903 

6-20 

3.5 

9.6 

7 

440 

1427 

987 

4 

12.57 

8 

672 

2144 

1472 

5 

19.6 

10 

1352 

4220 

2870 

The  diagram  of  curves,  giving  similar  information,  is  also  of  use. 
Actually,  the  weight  of  the  case  or  buoy  in  air  always  exceeds  that  of 
the  bare  shell  on  account  of  the  double  thickness  at  the  joints,  and 
because  the  cases  are  generally  strengthened  by  rings  of  J.  or  L  irons, 
and  the  mouth  of  the  case  or  buoy  by  a  ring  of  wrought  iron,  malleable 
cast  iron,  or  steel.  The  weights  of  these  additions  must  therefore  be 
deducted  from  llie  Iniovancv  recorded  in  Inst  cohniin  of  Table  XX. 


Effects  of  Tidal  Currents. 


61 


As  regards  size,  the  available  buoyancy,  i.e.,  tliat  wliiuli  remains 
after  deducting  all  the  weights  which  have  to  be  supported,  should  be 
ample  to  prevent  the  system  being  drawn  down  by  tidal  currents  below 
the  limiting  horizontal  plane  of  action  of  the  ship's  bottom. 

This  can  be  insured  with  a  small  buoyancy  if  the  system  be  moored 
on  a  span  by  two  sinkers  or  anchors — one  up,  the  other  down  stream. 
The  system  then  remains  ii\  one  position  whether  the  tidal  current  run 
up  or  down  stream,  as  well  as  during  slack  water. 

Such  an  arrangement  is  well  adapted  for  a  mine  tired  by  an  observer 
or  observers  at  a  distance,  but  there  is  not  the  same  necessity  to  keep 
a  contact  mine  exactly  in  one  place,  and  there  are  certain  practical 
difficulties  in  laying  mines  on  two  moorings.      The  single  mooring  has 


ocale  oF  diameters  in  Feet 


therefore  been  adopted  for  contact  mines  in  Europe,  but  the  following 
calculations  will  show  how  difficult  it  is  to  use  such  mines  so  moored  in 
tidal  currents.  Assume  that  the  charge  of  explosive  is  100  lb.,  and 
that  the  weight  of  the  circuit-closing  apparatus  with  its  metal  envelope 
together  with  the  weight  in  sea  water  of  the  mooring  cable  and  mooring 
line,  with  shackles,  attachment  chains,  &.C.,  amount  to  100  lb.  more, 
total,  200  lb.  deadweight.* 

Let  the  depth  be  eleven  fathoms  at  low  water,  draught  of  vessels  to 
be  four  fathoms,  rise  and  fall  of  tide  two  fathoms,  and  centre  of  mine 
always  covered  by  one  fathom,  i.e.,  at  low-water  slack.  Evidently  the 
mine  must  not  be  more  than  four  fathoms  below  the  surface  just  before 
and  just  after  high  water  when  the  tidal  current  is  running. 

•  If  the  service  circuit-closer  and  mouthpiece  were  used,  this  deadweight 
would  be  considerably  greater. 


62  Submarine  Mining. 

Tlie  conditions  being  plotted  geometrically  (.see  diagram,  Fig.  26)  it 
will  be  found  that  the  angle  a  which  the  mooring  line  makes  with  the 
vertical  is  about  24  deg.  If  B  denote  the  available  buoyancy  of  the 
mine  when  loaded  and  moored,  and  if  P  denote  the  side  pressure  in 
pounds  on  the  mine  caused  by  the  current,  and  P^  the  pressure  on  the 
mooring  line  and  cable ;  then,  taking  moments  round  the  sinker, 
4.2B-9P-4.5  Pi  =  0. 

The  resistance  P  in  pounds  offered  by  a  .sphere  to  salt  water  flowing 
past  it  with  a  velocity  V  in  knots  per  hour  is 

P=1.03  V- A, 
wliere  A  is  the  area  in  square  feet  of  the  diametric  plane  {cide  letter 
from  the  late  Mr.  W.  Froude,  extracts  from  which  will  be  given  later). 

Also,  the  resistance  offered  by  an  upright  cylinder  under  the  same 
conditions  is 

P'  =  2.85  V2  A', 

Assume  that  the  mine  is  large  enough   to  keep  the  mooring  line 

nearly  straight,   and  that  the  resistance   offered   by  a    long    cylinder 

(length  =  I),  when  tilted,  is  approximately  equal  to  that  offered  by  a 

vertical  cylinder  whose  length  is  I  cos  a.     The  vertical  component  for 

the  wire  rope  will  be  60  x  0.9  ft.,  and  as  the  electric  cable  has  Jj-  slack, 

its  vertical  component  will  be  65  x  0.9  ft.     The   diameter  of  the  wire 

2  8 

rope  is ft.,    and    that   of  the  electric  cable  ft.       Conse- 

3x12  10x12 

quently 

Pi  =  2.85  V-f  60x0.9x       "     +65x0.9x ^    Vl9-66  V^ 

V  ::<  X  12  10  X  \2) 


[In  place  of  taking  moments  round  the  sinker,  the  formula 
B  =  V-  cot  a  (1.03  A+ 1.42  A') 
may  be  employed,  and  the  same  result  obtained.] 

Now  B=-L(9Px4.5F) 

4.2' 

=  V=  (2.21A  +  21.1). 
And  wlien  V  =  2  knots  per  hour, 

B  =  8.83  A  +  84. 
And  when  V  =  3  knots  per  hour, 

B::=20  A +190. 
And  when  V  =  4  knots  per  hour, 

B  =  35.3  A +  337. 
And  when  \'  =  5  knots  per  hour, 

B  =  55.1  A  +  527. 
As  before  stated,  however,  the  real  buoyancy  of  the  case  must  hold 
up  200  lb.   in  addition  to  its  own  weight.     The  actual    buoyancy  of 
the  mine  case,  wlien  empty,  must  therefore  be  : 


Baoijancij  Reqali'cd.  63 

For  a  2-knot  tide  =  8.8  A  +  284 
„  3  „  =  20  A  +  390 
,,  4  ,,  =3.5.3  A  +  537 
,,     5        ,,         =.55.1A  +  727 

Referring   to   tlie   tabU;  of   Imoyaucy,   etc.,  for  sttu;!  spherical   cases, 

whose  thicknes.s  <  =  — ,  it  will  be  found  that  the  al)0ve  e(iuatious   ai-e 

satisfied  wlien  D  (the  diameter  of  the  case)  is   2.4  ft.  for  a  2-kuot  tide, 
2.8  ft.  for  3  knots,  3.25  ft.  for  i  knots,  and  3.8  ft.  for  5  knots. 

These  figures  woukl  have  to  be  increased  if  the  cases  were  manu- 
factured in  the  manner  practised  in  this  country,  viz.,  if  several  heavy 
iron  strengthening  rings  are  added  to  the  interior  of  the  cases.  These 
rings  weigh  about  100  lb.  in  the  3-ft.  cases,  but  their  enijiloynient  is 
entirely  uncalled  for  in  spherical  cases,  either  as  a  manufacturing 
necessity  or  as  an  assistance  to  withstand  the  shock  of  countermines. 
The  same  amount  of  metal  added  to  the  thickness  of  the  skin  of  the 
case  is  evidently  a  much  better  method  of  employing  it.  There  is  no 
difficulty  in  forming  a  lap  joint  at  the  junction  of  the  two  hemispheres. 
But  the  question  of  available  buoyancy  requires  further  investigation 
before  entering  upon  the  methods  of  manufacture.  The  instance  given 
was  one  in  which  no  especial  difficulties  arose,  yet  the  size  of  the  case 
required  for  a  5-knot  current,  and  even  for  a  4-knot  current,  was  larger 
than  those  which  are  usually  employed  for  contact  mines,  and  every 
endeavour  should  be  made  to  decrease  their  size  for  the  reasons 
given  already,  on  pages  56  and  57.  But,  in  the  first  place,  it  will 
be  well  to  note  how  utterly  all  contact  mines  must  fail  when  the 
rise  and  fall  of  tide  exceeds  two  fathoms  or  thereabouts,  and  when  the 
method  of  single  mooring  is  adhered  to.  In  the  last  example,  if 
the  rise  and  fall  of  tide  be  three  fathoms  instead  of  two,  and  the  other 
conditions  remain  as  before,  it  is  evident  that  when  the  tidal  currents 
are  flowing  just  before  and  just  after  high  water  (and  they  frequently 
run  very  hard  at  the  first  of  the  ebb  out  of  a  large  land-locked  hai-bour) 
the  mines  will  be  submerged  five  fathoms,  and  will  consequently 
be  out  of  the  plane  of  action  of  a  vessel's  bottom  drawing  four  fathoms 
or  thereabouts.  Assuming  that  the  mines  are  only  drawn  down  one 
fathom  by  the  action  of  the  current,  double  mooring  would  only  have 
this  advantage  of  one  fathom  ;  but  it  is  very  important  in  a  large 
percentage  of  tidal  harbours,  where  the  rise  and  fall  of  tide  exceeds 
two,  but  does  not  exceed  three  fathoms.  When  it  exceeds  three 
fathoms  it  is  necessai-y  to  adopt  some  of  various  devices  which  will  be 
explained  hereafter.  But  the  rise  and  fall  may  be  moderate,  and  yet 
the  tidal  currents  and  the  depth  of  water  be  considerably  greater  than 


04  Siibmarine  Mining. 

in  the  instance  examined.  Such  conditions  are  met  with  at  tlie 
entrance  of  the  Solent.  Assume  that  the  depth  is  twenty-one  fathoms 
in  place  of  eleven  as  before  ;  then,  other  conditions  remaining  unaltered, 
it  will  be  found  by  geometrical  construction  that  when  a  single  mooring 
is  employed  a  =  18  deg.,  and  that,  taking  moments  round  the  sinker, 

5.8B-19P— 9.5P'  =  0. 

P'  found  as  before  =  2.85  V=  (6  +  7.8)^49.33  V^. 

And  P  as  before  =  1.03  V»  A. 

Consequently,      B  =  —   {19P  +  9.5P^) 

=  V2  (3.38  +  80.8). 
And  when  V  =  2  knots  per  hour, 

B=13.5  A  +  323. 
And  when  V  =  3  knots  per  hour, 

B  =  30.2  A +  727. 
And  when  V  =  4  knots  per  hour, 

B  =  54  A+1292. 
And  when  V  :=  5  knots  per  hour, 

B  =  84.2  A +  2020. 

But  the  actual  buoyancy  must  hold  up  50  lb.  more  cable  and  mooring 
line  than  in  the  last  example,  or  a  total  of  250  lb.  in  addition  to  the 
weight  of  the  case,  and  the  above  equations  therefore  become  when  so 
adjusted  : 

B=  13.5  A+   573  for  a  2-knot  current. 
=  30.2  A+  977     „    3 
==54     A  +  1542     „     4 
=  84.2  A  + 2270     „     5 

Referring  to  the  Table  we  find  that  these  equations  are  satisfied  when 
D  (the  diameter  of  the  case)  is  3.1  ft.  for  a  2  knot  tide,  3.9  ft.  for  3 
knots,  4.9  ft.  for  4  knots,  and  as  this  is  too  large  a  case  for  practical 
use,  it  is  unnecessary  to  work  out  the  figures  for  a  5-knot  tide. 

We  will  now  apply  a  mine  on  double  moorings  to  the  hist  example, 
and  note  the  results. 

A  glance  at  the  diagram  Fig.  26  shows  that  the  mine  can  be  sul)- 
merged  two  fathoms  at  low  water,  if  the  rise  and  fall  of  tide  be  no 
greater  than  two  fathoms.  Such  a  mine  is  therefore  less  likely  to  be 
seen  at  low-water  slack  than  a  mine  on  single  mooring  which  must, 
under  tiie  same  conditions,  rise  one  fatliom  higher  at  this  time  of  tide, 
if  moored  to  catch  a  four-fathom  vessel  at  all  times.  Another  and  a  very 
important  practical  advantage  in  favour  of  two  moorings  is  also  shown 
upon  the  same  diagram.  Before  laying  mines  on  single  moorings,  it  is 
necessary  to  survey  the  waters  to  be  mined  with  the  greatest  accuracy, 
and  subsequently  to  lay  tlie  mines  exactly  in  the  positions  where  sound- 
ings have  been  taken.     Wlien   the  sea    bottom  is  irrcirular   it  is  most 


Minei^  on  Txvo  Moorings. 


65 


difficult  to  lay  the  mines  at  the  correct  level,  and  in  spite  of  every 
precaution  they  often  have  to  be  raised  and  their  positions  sliifted  or 
their  mooring  lines  altered  in  length. 

When  mines  are  moored  each  on  a  span  between  two  sinkers,  or 
between  an  anchor  and  a  sinker,  a  very  accurate  survey  of  the  waters 
to  be  mined  is  less  essential,  because  the  submersion  of  the  mines  can 
be  rectified  when  laying  the  last  sinker,  and  any  irregularity  of  sea 
bottom  is  automatically  allowed  for  in  this  process.  Thus,  the  anchor 
A  (Fig.  26)  being  laid  first  by  means  of  its  wire  rope  mooring  line,  the 

High    \IVater  levd . - 


D'o^ram   showing  Mine  on  Sing 

mine  is  allowed  to 


&.  Mine   on  Double  mooring  at  depths  of  21  &  II   fathoms. 

oat  on  the  surface.  The  mooring  steamer  then 
drops  down  with  the  current,  keeping  its  head  up  stream,  pointing  on 
the  position  of  the  anchor,  and  paying  out  the  electric  cable.  The 
sinker  is  now  lowered  by  a  line  until  it  touches  the  bottom,  and  the 
electric  cable  is  slacked  off  at  the  same  time.  A  boat  attends  at  the 
mine,  and  attaches  a  measuring  line  to  it.  The  steamer  then  adjusts 
the  position  of  the  sinker  until  the  mine  is  at  the  required  submersion, 
which  of  course  varies  with  the  time  of  tide.  The  boat  hails  when  the 
desired  result  is  obtained,  the  end  of  the  line  is  then  stoppered  to  the 
cable,  which  is  paid  out  and  taken  by  the  steamer  to  any  desired 
place.  If  the  bottom  be  level  the  sinker  will  be  placed  at  S',  the  span 
being  equally  divided.  But  if  the  bottom  be  irregular,  as  shown  in 
diagram,  the  sinker  will  be  placed  at  S  and  the  two  mooring  lines  will 
take  slightly  different  tilts.  To  facilitate  this  operation  a  heavy  sinker 
should  be  used  at  S,  and  the  angle  between  the  lines  at  the  mine  should 
not  be  much  less  than  a  right  angle.  A  good  spread  in  tlie  span  also 
decreases  the  necessary  buoyancy  of  the  mine. 

The  following  calculations  give  the   size,  kc,   of  a  detached   circuit- 


66  Submarine  Mining. 

closer  moored  on  a  span  as  shown,  and  supporting  4  ft.  below  it  a  small 
mine  containing  36  lb.  of  blasting  gelatine  in  a  case  weighing  10  lb.  in 
salt  water,  or  46  lb.  when  loaded.*  The  circuit-closing  apparatus  with 
envelope  to  weigh  20  lb.  Tlie  buoy  to  be  spherical,  and  of  steel,  witli 
a  thickness  equal  to         .     The  mine  to  be  moored  by  the  electric  cable 

on  one  side  and  a  steel  wire  rope  on  the  other  side  to  two  anchors  or 
sinkers  up  and  down  stream.  The  cable  to  be  armoured,  and  to  weigh 
25.5  cwt.  per  knot  in  air,  and  13  cwt.  per  knot,  or  1.45  lb.  per  fathom, 
in  salt  water.  Its  diameter  to  be  about  0.8  in.,  and  its  breaking 
strength  5  tons.  The  wire  rope  to  be  0.6  in.  in  diameter,  to  weigh 
3  lb.  in  air,  and  2.5  lb.  in  salt  water  per  fathom ;  also  to  possess  a 
breaking  strength  of  about  5  tons. 

When  moored  in  21  fathoms,  the  buoy  will  therefore  have  to  support 
27  (1.45 +  2.5)  =  108  lb.  of  cable  and  rope,  as  well  as  46  1b.  for  tlie 
small  loaded  mine,  or  154  lb.  in  all,  besides  its  own  weight.  Also,  the 
area  of  the  diametric  plane  opposing  the  current  is  for  the  cable  = 

8  6  ^ 

27  X  6  X  jjj — ,  .5  cos  45,  and  for  tlie  rope  27  x  6  x  Jq^^  cos  45.     Con- 
sequently the   total  vertical   area  given   by  the   cable  and   rope  =  13.4 
square  feet,  and  the  small  mine  case  offers  half  a  square  foot. 
Proceeding  as  in  previous  examples  : 

19  B-19P-18P"-9.5]'i  =  0. 
When  B    =  available  buoyancy  of  sphere, 

P    =  side  pressure  on  same, 

P"  =same  on  small  mine  case, 

pi  =  same  on  cable  and  rope. 


IS 

.-.  B 

=  P+j9P»  +  iP'. 

But 

P 

=  1.03  V=  A. 

When 

A 

=  diametric  area  of  the  sphen 

and 

P" 

=  2.85  V- 4, 

and 

Pi 

=  2.85  V-  13.4. 

Hence 

B 

=  V- (1.03  A +  23.25). 

When 

V 

=  2  knots  per  hour, 

B 

=  4.12  A  +  93. 

When 

V 

=  3  knots  per  hour, 

B 

=  2.27  A +  209.25. 

When 

V 

=  4  knots  per  hour, 

B 

=  16.48  A +  372. 

When 

V 

=  5  knots  per  hour, 

B 

=  25.75  A +  58 1.25. 

r.iit,    as   already   stated,    the  actual    buoyancy  of    the   splicro    must 

*  This  calculation  should  be  slightly  iiioditicd  (see  footnote  p.  5!)).  but  the 
rpsults  are  not  materially  attected. 


Froude's  Formuke. 


67 


be  gre.ater  tlinn  the  above  by  154  lb.     The  buoyancy  so  altororl  then 
=   4. 1 2  A  +  247  for  a  2-knot  tide. 
=  9.27  A +  368     „     3 
=  16.48  A +  526     „     4 
=  25.75  A  +  735    „    5 

Referring  to  the  Table  we  find  that  tliese  equations  are  satisfied 
when  D  (the  diameter  of  the  buoy  or  detached  circuit-closer)  is  2.3  ft. 
for  a  2-knot  tide,  2.G  ft.  for  3  knots,  3.1  ft.  for  4  knots,  and  3.5  ft.  for 
5  knots. 

Comparing  these  results  with  those  calculated  for  the  service  arrange- 
ment under  like  conditions  (depth  of  water,  draught  of  vessel,  &c.),  we 
find  as  follows  : 

Table  XXI. 


Size  of  Sphere  Required,  Diameter,  Feet. 

per  Hour. 

Single  Mooring. 

Double  Moorings. 

2 
3 
4 
5 

3.1 
3.9 
4.9 

Not  calculated 

2.3 
2.6 
3.1 
3.5 

From  this  we  see  that  a  service  case,  &c.,  cannot  be  used  in 
21  fathoms  when  current  exceeds  2  knots.  But  with  two  sinkers 
and  everything  made  as  light  as  possible,  yet  possessing  sufficient 
strength,  a  3-ft.  sphere  will  act  efiectively  in  the  same  depth  in  a 
current  of  nearly  4  knots.  Also  a  2i-ft.  sphere  in  21  fathoms  and 
3  knots.  Also  a  similar  calculation  will  prove  that  a  2|-ft.  sphere 
will  act  efficiently  in  a  3^-knot  current,  and  a  depth  of  11  fathoms. 
Evidently  two  moorings  should  be  used  with  each  mine  exposed  to  a 
strong  tidal  current. 

The  Late  Mr.  W.  Froude's  Formulm  for  Side  Pressure. — It  will  now 
be  convenient  to  quote  from  the  valuable  letter  written  by  the  late  Mr. 
W.  Froude,  May  18,  1876,  and  already  refen-ed  to  :  "  Sir, — I  have  read 
with  interest  and  attention  your  letter  of  the  16th  and  its  inclosures 
relating  to  the  forces  to  which  a  submarine  buoyant  torpedo  is  subject 
when  moored  in  a  tideway  or  current  of  known  velocity,  and  I  will  in 
reply  gladly  give  you  all  the  relevant  information  I  possess,  though  I 
regret  to  say  that,  in  the  way  of  positive  information,  the  amount  to  be 
given  is  not  large,  the  fact  being  that  the  existing  state  of  knowledge 

on  the   subjects  in  question  is  very  incomplete In 

dealing  with  the  force  impressed  on  bodies  by  the  water  flowing  past 
p2 


68  Submarine  Mining. 

them,  I  hope  1  shall  not  appear  too  dogmatic  or  self-confident  when  I 
state  that  experiment  and  improved  theory  alike  show  that  the  re- 
sistance of  such  bodies  as  foruiulated  in  the  ordinary  text-books 
whetlier  mathematical  or  practical,  or  on  hydraulics,  are  almost 
invarial)ly  founded  on  erroneous  hypotheses,  and  are  incorrect.  To 
begin  witli,  it  is  usually  stated  that  the  resistance  to  a  plane  moving 
at  right  angles  to  itself  through  an  inelastic  fluid  is  equal  to  the  weight 
of  a  column  of  the  fluid  having  a  sectional  area  equal  to  the  area  of  tlie 
plane,  and  a  length  equal  to  the  height  due  to  the  velocity ;  and  it  is  on 

this  assumption  that  Molesworth's  coefficient is  founded. 

Beaufoy's  experiments  long  ago  proved  conclusively  that  the  real  re- 
sistance exceeds  them  in  the  rates  of  1.10  or  1.12  to  0.976. 

"Again,    the   proposition    that the    resistance   to   a 

cylinder  moving  at  riglit  angles  to  its  axis,  is  half  the  pressure  there 
would  be  on  the  diametric  plane,  calculated  by  the  above  erroneous 
hypothe.sis,  is  also  an  entirely  mistaken  proposition. 

"lam  able,  from  experiments  of  my  own,  to  give  an  approximate 
measure  of  the  resistance  experienced  by  the  cylinder,  because  in  an 
investigation  of  the  pressure  log,  as  it  is  called,  which  I  carried  out  with 
tlie  Admiralty  experimental  apparatus,  I  ascertained  the  normal  pressure 
on  every  part  of  the  circumference  of  a  cylinder  thus  moving. 

"  On  analysing  this  series  of  pressures,  it  proved  that  their  longi- 
tudinal component,  that  is  the  component  in  tlie  line  of  motion,  or 
rather  the  integral  of  thin  longitudinal  components,  was  just  equal  to 
the  weight  of  a  column  of  water,  the  base  or  sectional  area  of  which  is 
the  diametric  plane  of  the  cylinder,  and  the  height  of  whicli  is  the 
height  due  to  the  velocity.  Tliis  component  is  not  quite  tlie  whole 
resistance,  for  there  must  be  added  the  component  due  to  the  circum- 
ferential drag  of  the  water  acting  by  surface  friction.  It  is  not  easy  to 
put  a  correct  value  on  this  addition,  because  the  speed  of  tlie  flow  of 
the  water  past  tlie  surface  of  the  cylinder  is  greatly  modified  by  proper 
stream-line  motion,  and  by  induced  eddies.  I  believe,  liowever,  that  it 
is  small  in  amount,  and  unless  tlie  surface  become  very  foul  it  may  bo 
neglected. 

"  Taking  the  resistance  in  pounds,  P ;  and  the  speed  in  knots,  V  ; 
and  tlie  area  of  the  diametric  plane  in  square  feet.  A, 

"  The  resistance  of  a  plane  moving  at  right  angles  to  itself  is  about 
P=3.2  V^A  in  fre.sh  water,  and  3.27  V'-A  in  salt  water. 

"  The  i-esistance  of  a  cylinder  moving  at  riglit  angles  to  its  axis  is 
about 

P  =  2.78  V-A  in  fresh  water,  and  2.85  V=A  in  salt  water. 

"  As  regards  the  resistance  of  a  sphere,  Beaufoy's  experiments  give 


Ruck's  Rise  and  Fall  System.  69 

the  result  conclusively  ;  I  mean  there  seems  no  reason  to  mistrust  their 

correctness.     According  to  them  we  have  as  the  resistance  of  a  sphere 

P=  1.0  V-A  in  fresh  water,  and  1.03  V-'A  in  salt  water. 

"  I  sliould  add  that  in  all  these  cases  it  appears  that  the  power  of  the 
velocity  to  which  the  resistance  is  proportional  is  rather  under  2,  in 
fact,  about  1.87  to  1.95." 

As  the  sphere  is  the  best  form  of  case  for  a  buoyant  body  used  in 
submarine  mining,  the  most  important  formula  of  those  given  above  is 
the  last ;  and  as  the  index  of  V  is  slightly  less  than  2,  the  constant  may 
be  reduced  to  unity,  and  the  formula  for  the  resistance  P  (lb.)  of  a 
sphere  whose  diametric  area  is  A  (sq.  ft.)  moored  in  salt  water  having 
a  velocity  V  (knots  per  hour)  becomes  : 
P  =  V-A. 

Difficulties  engendered  by  Rise  and  Fall  of  Tide.— It  will  be  noted  in 
the  example  illustrated  by  the  last  diagram  (Fig.  26)  that  when  the 
rise  and  fall  of  tide  approaches  or  exceeds  the  draught  of  the  vessels 
which  are  to  be  acted  upon  by  the  mines,  it  is  impossible  to  fulfil  all  the 
conditions  required.  Either  the  circuit-closing  buoys  (or  the  self- 
buoyant  mines  if  these  be  used)  must  be  so  moored  that  they  float  on 
the  surface  at  dead  low  water,  or  the  vessels  will  be  enabled  to  swim 
over  the  mines  at  high  water.  One  way  of  meeting  this  difficulty  is  to 
moor  the  contact  mines  which  are  nearest  to  the  mouth  of  a  harljour  in 
which  the  rise  and  fall  of  tide  is  considerable,  at  such  a  submersion  that 
they  will  act  during  the  lower  half  of  the  tidal  level ;  and  to  moor  the 
mines  further  up  the  harbour  so  that  they  will  act  during  the  upper 
half  of  the  tidal  level.  When  this  plan  is  followed  it  is  necessary  to 
use  a  larger  number  of  contact  mines  than  would  be  required  in 
a  harbour  with  a  moderate  rise  and  fall  of  tide,  and  in  order  to 
obviate  this  difficulty  a  number  of  attempts  have  been  made  to  design  a 
trustworthy  plan  whereby  the  mines  shall  rise  and  fall  automatically 
with  the  rise  and  fall  of  tide.  The  most  successful  arrangement  is  the 
following  : 

Eise  and  Fall  Mines  designed  by  Major  R.  M.  Ruck,  R.F.—ln  Figs. 
27  and  28,  A  represents  the  floating  body  or  mine,  B  is  a  counterpoise 
also  possessing  flotation,  0  is  a  chain  graduated  in  size  and  weight,  P  is 
a  pulley,  S  is  a  mooring,  and  D  is  a  mooring  rope  or  chain. 

B  may  be  a  metal  case  either  open  at  the  bottom  or  closed  by  a 
waterproof  diaphragm.  B  may  also  be  a  compressible  waterproof  closed 
bag,  suitably  weighted. 

0  is  a  chain  made  of  links  varying  in  weight ;  the  larger  links  being 
furthest  from  B.  A  chain  passing  through  the  pulley  is  not  indis- 
pensable ;  a  weighted  rope  may  he  used  with  the  heavier  end  rusting  on 


70 


Submarine  Mining. 


the  bottom,  A  and  B  being  connected  in  tliis  case  by  a  light  wire  rope 
passing  round  the  pulley.  Fig.  27  represents  the  system  at  low  water, 
and  Fig.  28  at  high  tide. 

In  shallow  water  two  pulleys  are  required  as  shown  in  Fig.  29,  and  in 
waters  where  the  depth  is  considerable  as  compared  with  the  rise  and 
fall  of  tide,  the  modifications  shown  in  Figs.  30,  31,  32,  can  be  adopted. 
When  an  electric  cable  is  attached  to  the  mine,  it  can  be  led  away  as 
shown  in  Fig.  34.     In  order  to  prevent  any  twisting  action  the  mooring 


FuqSZ. 


rope  of  the  mine  can  be  led  through  a  ring  or  rings  attached  to  the 
counterpoise  as  shown  in  Fig.  33.  Several  other  modifications  have 
heen  described  by  the  inventor,  but  the  simpler  forms  now  illustrated 
arc  prolKiljly  of  the  most  practical  value.  In  order  to  assure  success 
with  this  system,  care  must  be  takrii  in  tlie  manufacture  of  tiie  gear 
and  in  laying  the  mines. 

Tlic  action  is  as  follows  :  Cunnncnehig,  say,  at  low  water,  as  the  tide 


Spacmg  of  Cuntad  Mines.  71 

rises  the  increased  water  pressure  on  the  counterpoise  r(!cluces  its  dota- 
tion by  compressing  the  air  contained  in  it.  The  equilibrium  of  the 
system  is  overthrown  ;  B  sinks,  A  rises,  until  equilibrium  is  restored  by 
some  of  the  heavy  chain  passing  round  the  pulley  or  by  some  of  the 
weighted  rope  falling  and  resting  upon  the  ground.  Another  rise  of 
tide  occurs,  and  the  action  is  repeated.  A  fall  of  tide  produces  an 
action  in  the  opposite  direction.  By  these  means  the  mine  is  kept 
within  narrow  limits  at  a  constant  depth  below  the  surface.  The 
mine  and  the  counterpoise  should  be  so  arranged  that  they  never  touch 
one  another.  Should  this  occur  in  rough  weather  they  damage  one 
another. 

The  inherent  difficulties  of  the  problem  have  been  ingeniously  met  in 
this  solution  by  Major  Ruck,  but  the  gear  is  necessarily  heavier  and 
more  difficult  to  work  than  the  usual  arrangements,  and  the  mooring 
must  be  twice  as  heavy  as  usual.  It  is  never  necessary  to  employ 
automatic  arrangements  for  mines  to  catch  large  vessels  where  the  rise 
and  fall  of  tide  does  not  exceed  three  fathoms,  and  when  this  is  exceeded, 
the  tidal  currents  are  so  powerful  that  it  becomes  a  matter  for  con- 
sideration whether  to  adopt  automatic  rise  and  fall  mines,  or  to  employ 
a  larger  number  of  ordinary  mines  at  different  levels,  or  to  use  observa- 
tion mines  instead  of  mines  that  are  fired  by  contact.  The  local 
peculiarities  of  each  harbour  must  be  thoroughly  examined  before 
deciding  on  such  a  matter. 

Spacing  of  Electro-Contact  Mines. — -The  next  question  to  which  an 
answer  is  required,  refers  to  the  distance  that  should  separate  electro- 
contact  mines,  and  the  following  considerations  should  be  borne  in 
mind  before  a  reply  is  given. 

1.  The  mines  should  be  spaced  at  such  intervals  that  there  is  no 
danger  of  their  fouling  one  another  when  eddies  set  them  in  opposite 
directions. 

It  is  highly  improbable  that  these  eddies  will  ever  simultaneously  act 
in  such  a  manner  as  to  tilt  mines  on  single  moorings  so  that  the  angle 
a  with  the  vertical  (see  Fig.  26)  will  attain  18  deg.,  the  mines  being 
tilted  in  opposite  directions.  But,  assuming  that  this  extreme  case  is 
possible  and  that  the  length  of  the  mooring  line  is  also  extreme,  say  20 
fathoms  ;  then  the  mines  cannot  foul  each  other  if  the  sinkers  be  sepa- 
rated by  a  distance  of  12 J-  fathoms,  or  75  ft.  Other  considerations  to 
follow  will  show  that  electro-contact  mines  must  be  spaced  at  greater 
intervals  than  75  ft.;  but  the  above  is  important,  because  the  mine 
intervals,  whatever  they  may  be  fixed  at,  for  other  considerations  should 

12-^- 
be  increased  by  an  amount  not   exceeding  -^^  =0.625   of  the  vertical 


72  Submarine  Mining. 

length  of  the  mooring  line,  if  the  site  be  one  in  which  strong  sworls  or 
eddies  of  water  occur  at  any  time  of  tide. 

2.  The  mines  should  be  spaced  at  such  intervals  that  the  explosion  of 
one  mine  shall  not  damage  any  of  the  neighbouring  mines.  This  con- 
sideration shows  the  advantage  of  employing  the  smallest  effective 
charges  in  electro-contact  and  other  buoyant  mines. 

If  a  charge  of  72  lb.  of  blasting  gelatine  be  employed,  as  before  sug- 
gested in  foot-note  p.  59,  at  what  distance  will  the  spherical  circuit- 
closer  jacket  be  safe  from  damage  1 

As  already  shown,  a  3-ft.  sphere,  made  of  ;|-in.  steel,  should  with- 
stand a  collapsing  pressure  of  1400  lb.  on  the  square  inch;  and  it  has 
been  proposed  in  these  papers  to  make  all  spherical  cases  for  Ijuoyant 
mines,  circuit-closers,  &c.,  of  the  same  strength  to  withstand  such 
pressures. 

This  value  for  P  is  obtained  by  the  subaqueous  explosion  of  72  lb.  of 
blasting  gelatine  at  a  distance  of  about  50  ft.  horizontally  from  the 
charge,  as  calculated  by  the  author's  formula  already  given. 

Hence  to  meet  consideration  (2)  the  electro-contact  mines  under  dis- 
cussion must  be  spaced  apart  at  50  ft.  And  if  the  depth  of  water  be 
such  that  mooring  lines  10  fathoms  long  are  required,  0.6  x  60  ft.  = 
36  ft.  must  be  added  to  meet  consideration  (1).  The  total  spacing 
must  therefore  be  at  least  50  ft.  +  36  =  86  ft.  for  the  mines  under  dis- 
cussion. 

3.  The  mines  must  also  be  so  spaced  that  when  one  is  exploded  it  shall 
not  cause  the  neighbouring  mines  to  signal  as  if  struck  by  a  vessel,  for 
this  would  cause  them  to  explode  also,  and  thus  the  whole  of  the  electro- 
contact  mines  in  one  group  might  be  exploded  simultaneously,  when 
only  one  should  explode.  Electrical  arrangements  can,  however,  be 
made  on  shore  at  the  firing  station,  wdiich  will  prevent  this  undesirable 
result,  and  the  matter  need  not  be  further  discussed  here  except  to 
state  that  even  in  the  absence  of  such  electrical  safeguard,  there  is 
no  practical  difficulty  in  so  adjusting  the  circuit-closing  arrrangements 
of  the  mine,  that  no  signal  of  a  neighbouring  mine  shall  be  caused  by  a 
mine's  explosion  when  the  mines  are  spaced  at  intervals  of  100  ft.,  the 
minimum  spacing  for  electro-contact  mines  should  therefore  be  136  ft., 
when  the  charges  are  limited  to  the  amount  stated.  As  this  distance 
will  also  meet  considerations  (1)  and  (2)  in  the  example  taken,  it  may 
be  accepted  for  depths  up  to  10  fathoms.  Beyond  this  depth  the  spaces 
between  tiie  mines  should  be  slightly  increased,  say  to  150  ft. 

4.  There  yet  remains  another  matter  of  some  practical  importance 
that  bears  upon  this  question,  viz.,  tlie  length  and  handiness  of  the 
steamer  employed  for  laying  the  mines.     After  a  long  txpcricnco  I  am 


Jhrmant  Mines.  73 

convinced  th;it  tlio  Icngfli  of  such  a  cnift  ouglit  not  to  exceed  70  ft.,  nnd 
she  should  be  a  very  handy  sliip.  If  tlic  mooring  steamer  be  90  ft.  or 
100  ft.  long,  she  is  liable  to  foul  and  drag  tlie  mines  already  laid,  when 
carrying  out  the  mooring  operations.  Tliis  difficulty  is,  however, 
avoided  by  wliat  is  termed  the  dormant  system,  which  will  now  be 
described. 

Dormant  Electro-Contact  Alines. — It  will  fi'equently  occur  that  mines 
must  be  laid  in  channels  which  cannot  be  closed  to  commerce  or  to  tlie 
frequent  passage  of  friendly  war  vessels,  and  yet  it  may  be  very  desir- 
able to  employ  electro-contact  mines  rather  than  observation  mines  for 
which  there  may  be  no  suitable  sites  for  observing  stations  in 
the  vicinity  of  the  said  channels.  Under  the  above  conditions  the 
ordinary  electro-contact  mines  are  evidently  inapplicable,  as  they  would 
be  cut  away  and  destroyed  by  the  screws  of  passing  steamers,  and  might 
even  be  accidentally  exploded,  if  the  detonating  fuzes  were  subjected 
to  severe  blows.  Buoyant  mines  can  then  with  advantage  be  moored 
in  such  a  manner  that  they  are  held  down  to  the  bottom  until  they 

F{x}.35.  Fiq.SG. 


are  required  to  rise  into  the  positions  required  to  prevent  the  passage 
of  hostile  vessels.  They  are  then  called  dormant  mines.  The  plan  can 
be  employed  in  connection  with  mines  on  a  single  mooring  and 
sinker,  or  with  mines  on  a  double  mooring  or  bridle  and  two  sinkers, 
or  with  mines  arranged  on  Major  Ruck's  system,  as  shown  on  Figs.  35  and 
36,  in  which  L  L  are  explosive  links  tired  by  a  suitable  electric  current 
in  such  a  manner  that  the  mines  are  not  exploded  when  the  links  are 
exploded.  The  other  letters  on  these  figures  refer  to  the  articles 
similarly  lettered  and  already  described  in  the  rise  and  fall  system  of 
electro-contact  mines.  When  but  one  sinker  is  used,  precautions  must 
be  taken  to  prevent  the  slack  portion  of  the  mooring  line  from  fouling 
the  rest  of  the  gear,  or  the  mine,  Ac,  will  not  rise  into  tlie  proper  place 
when  the  explosive  link  is  fired.  One  method  that  suggests  itself  is 
to  coil  the  slack  of  the  mooring  lino  on  the  top  of  the  sinker,  or  around 


74 


Submarine  Mining. 


it,  and  to  tie  the  coil  with  weak  stoppers,  which  the  buoyancy  of  the 
mine,  Ac,  can  break  as  soon  as  the  link  is  hrecl. 

Another  plan  that  suggests  itself  is  to  coil  the  slack  on  a  wooden 
drum,  one  end  of  which  is  secured  to  the  sinker  by  a  short  piece  of 
rope,  and  the  other  by  an  explosive  link.  On  the  latter  being  lired  the 
drum  would  tilt  into  a  vertical  position,  and  the  mooring  line  be 
released. 

When  a  mine  is  mooi'ed  on  a  bridle  between  two  sinkers,  an  eye  can 
be  formed  two  or  three  fathoms  down  the  wire  rope  mooring  line,  and 
the  mine  be  secured  to  it  by  an  explosive  link.  This  is  a  simple 
arrangement,  and  the  dormant  system  therefore  seems  to  be  well  adapted 
for  mines  moored  in  this  manner. 

The  explosive  link  was  first  suggested  by  the  author  when  carrying 


Bletric  Wires, 
Fl^dl    I        OlandNut 


out  the  experiments  against  H.M.S.  Oberon,  and  was  afterwards  em- 
bodied in  his  mechanical  system  of  submarine  mines.  Tlie  links  consist 
of  short  iron  or  metal  tubes  containing  a  small  bursting  charge  and  an 
electric  fuze ;  also  suitable  water-tight  entrances  for  the  electric  wires 
and  metal  eyes  cast  on  the  body  of  the  tube  to  take  the  necessary 
shackles  or  wire  lashings.  The  interior  should  be  turned  out  where  the 
india-rubber  plug  rests,  to  insure  a  water-tiglit  joint.  A  bursting 
charge  of  1  drachm  of  rifle  powder  is  suflicient,  the  body  being  I  in. 
thick  if  made  of  cast  iron,  and  I  in.  thick  if  made  of  brass.  The 
electrical  arrangements  in  the  mine  and  circuit-closer  are  such  that 
the  explosive  link  for  any  particular  mine  can  be  fired  when  it  is 
desired    to    do    so   without    firing    the    mine    itself,    although   a    single 


Manufacture  of  Buoyant  Cases.  7o 

cable  is  used.     Tlic  electrical  details  for  electro-contact  and  other  mines 
must  be  explained  hereafter. 

Manufacture  of  Cases  for  Electro-Contact  Mines. — The  size  antl 
thickness  and  shape  of  the  cases  having  been  settled,  after  a  decision 
has  been  arrived  at  concerning  the  nature  of  the  explosive  to  be 
employed,  no  important  difficulty  is  likely  to  arise  in  their  manu- 
facture. Siemens  Landore  steel  is  usually  employed,  the  hemispheres 
being  pressed  into  shape  when  hot  by  stamps  worked  by  hydraulic 
rams.  It  is  usual  to  secure  eyes  by  means  of  palms  ri vetted  to  the 
case  afterwards,  but  these  palms  are  a  source  of  trouble,  the  cases 
being  apt  to  leak  at  the  palms,  after  any  rough  handling  to  which 
they  may  be  unavoidably  subjected.  It  is  easy  to  avoid  the  use  of 
such  eyes,  providing  instead,  two  wire  rope  rings  in  which  eyes  are 
made,  and  connecting  these  rings  by  wire  rope  bracing  as  shown  on 
Fig.  38. 


Another  point  of  weakness  in  buoyant  cases  for  submarine  mining  is 
the  existence  of  rivetted  joints  ;  for  although  it  is  easy  enough  to  make 
the  joints  water-tight  so  as  to  withstand  ordinary  rough  usage,  it 
must  be  borne  in  mind  that  such  cases  have  to  remain  water-tight  after 
receiving  the  severe  blows  occasioned  by  mines  exploding  in  their 
vicinity.  Rivetted  joints  should  therefore  be  avoided  if  possible, 
because  a  small  leak  soon  causes  the  mine  case  to  fill  and  to  sink. 

Tinned  joints  would  be  absolutely  water-tight,  should  be  as  strong  as 
rivetted  joints,  and  would  be  lighter.  Rivetted  joints  are  apt  to  leak 
because  that  portion  of  the  case  being  more  rigid  than  the  remainder, 
any  indentation  caused  by  a  neighbouring  explosion  is  apt  to  pull  open 
the  joint  by  bending  the  steel  plate  inwards  away  from  the  joint,  and 
outwards  at  the  joint  or  caulking,  tlie  lino  of  rivets  being  tlie  fulcrum. 


76  Submarine 

With  a  tinned  joint,  the  lips  would  be  the  strongest  portion  of  the  con- 
nection. 


As  regards  the  mine  cases  in  Division  2,  Class  A,  viz.,  those  not 
under  control  and  coming  under  the  generally  accepted  name  of 
"  mechanical  mines"  (although  some  are  electrical  and  others  chemical), 
they  are  generally  made  as  cheaply  as  possible  so  that  their  numbers 
may  compensate  for  inferior  individual  efficiency  as  compared  with 
the  mines  under  control.  Moreover,  inasmuch  as  they  must  be  spaced 
at  such  intervals  that  the  explosion  of  one  shall  not  cause  the  neigh- 
bouring mines  to  act,  the  cases  can  be  much  weaker  than  those  for 
electro-contact  mines  where  electrical  arrangements  can  be  introduced 
to  prevent  such  self-destruction.  As  "  mechanical  mines "  will  be 
examined  in  a  separate  chapter,  no  more  need  be  said  at  present  about 
them. 

The  manufacture  of  the  cases  for  large  buoyant  mines  will  be  treated 
in  the  next  chapter. 


77 


CHAPTER    VI. 

Large  Mines. 
The  cases  required  for  Class  B  mines,  viz.,  those  that  contain  large 
charges  and  act  at  a  distance  from  the  target,  will  now  be  considered. 

All  these  mines  are  necessarily  in  Division  1  ;  i.e.,  are  under  control, 
and  are  therefore  electrical  mines.  But  they  can  be  conveniently 
divided  into  two  sub-divisions  :  (1)  Ground  mines,  which  lie  on  the 
bottom  ;  (2)  buoyant  mines. 

Ground  mines  are  invariably  used  in  preference  to  the  latter  when 
the  depth  of  water  is  not  excessive. 

French  Systei7i.—As  before  stated,  the  French  appear  to  use  ground 
mines  up  to  depths  of  80  ft.,  the  charges  being  : 
Table  XXII. 
550  lb.  gun-cotton,  or  2200  lb.  gunpowder,  26  ft.  to  36  ft. 
660        ,,         ,,  3300        ,,         ,,  up  to  50  ,, 

880        „         „  4400        ,,         „  ,,     60  „ 

1100        ,,         „  "     ^'^  " 

1320        „         „  "     73  „ 

1540        ,,         ,,  "    80  ,, 

English  System.—The  English  custom  has  remained  practically 
unaltered  since  1873,  when  Lieutenant-Colonel  R.  H.  Stotherd's  book, 
"  Notes  on  Submarine  Mines,"  was  published  in  England  and  repro- 
duced soon  afterwards  by  an  enterprising  publisher  in  New  York, 
U.S.A.  The  charges  for  ground  mines  therein  mentioned  for  the 
following  depths  are  : 

Table  XXIII. 

250  lb.  gun-cotton,  20  ft.  to  35  ft. 

500        „        „         35  „        60  „ 

When  the  water  is  over   60  ft.  in  depth,  500  lb.  buoyant  mines  are 

used,  and  are  moored  about  48  ft.  from  the  surface.     These  charges  and 

limits  were  not  altered  after  the  completion  of  the  series  of  experiments 

against  the  Oberon. 

American  System.— It  is  believed  that  the  limit  of  size  of  mine 
charges  in  the  American  service  has  been  fixed  at  400  lb.,  and  that 
American  adepts  prefer  to  employ  a  number  of  moderate  charges  rather 
than  a  few  large  mines.     But  the  arguments  (already  advanced  in  the 


78  Submarine  Mining. 

paper  on  contact  mines  in  this  series)  advocating  the  employment  of 
the  minimum  eflective  charges  when  the  mines  are  buoyant,  do  not 
apply  when  tlie  mines  rest  on  the  bottom ;  for  there  is  then  no  diffi- 
culty whatever  in  making  the  cases  very  strong  to  resist  neighbouring 
explosions,  and  when  the  mines  are  lired  by  observers  at  a  distance  the 
large  mines  are  more  likely  to  act  in  tlie  desired  manner,  on  account  of 
larger  area  of  effect. 

Small  charge  observation  mines  cannot  therefore  be  recommended, 
except  in  comparatively  shallow  waters,  which  are  situated  near  to  the 
observing  stations — and,  as  a  rule,  these  waters  can  be  mined  more 
effectively  by  electro-contact  mines — or  by  small  ground  mines  with 
detached  circuit-closers.  A  250-lb.  mine  charged  with  gun-cotton 
possesses  an  effective  striking  power  up  to  distances  of  20  ft.  from  its 
centre ;  consequently  its  effective  circle  for  observation  firing  must 
always  be  less  than  40  ft.  in  diameter,  which  maximum  would  only  be 
attained  by  a  ground  mine  when  the  vessel  attacked  is  wall-sided,  flat- 
bottomed,  and  drawing  nearly  the  full  depth  of  the  mined  water. 
These  considerations  must  make  it  evident  that  ground  mines  with 
charges  not  exceeding  250  lb.  gun-cotton  are  only  adapted  for  observa- 
tion firing  at  very  close  quarters. 

Ground  Mines  Fitted  with  Detached  Circuit-Closers. — Small  ground 
mines  can,  however,  be  usefully  employed  when  they  are  fired  by  means 
of  a  detached  circuit-closer  moored  above  them.  For  instance,  the 
250-lb.  gun-cotton  ground  mine  would  act  well  in  water  up  to  45  ft. 
against  vessels  drawing  25  ft.  and  over,  the  detached  circuit-closer 
being  20  ft.  above  the  bottom  ;  and  if  blasting  gelatine  were  used  in  the 
same  cases  they  would  be  effective  up  to  depths  of  53  ft.  Similarly,  a 
ground  mine  charged  with  500  lb.  of  gun-cotton,  if  fired  by  a  detached 
circuit-closer  moored  38  ft.  above  it,  that  being  the  striking  distance 
of  such  a  mine  against  an  ironclad,  would  be  effective  against  vessels  of 
25  ft.  draught  and  over  in  waters  up  to  63  ft.,  and  if  blasting  gelatine 
wore  used  the  mines  would  act  up  to  depths  of  78  ft.  But  the  employ- 
ment of  detached  circuit-closers  in  connection  with  mines  containing 
large  charges  has  to  a  great  extent  gone  out  of  fashion,  because  such 
mines  are  generally  placed  in  those  deeper  portions  of  a  harbour  which 
cannot  conveniently  be  obstructed  by  buoyant  bodies  which  may  foul, 
or  be  tliemselves  damaged  by  passing  vessels  that  are  not  foes.  This 
objection  can,  however,  be  readily  met  by  the  dormant  system  of 
mooring  mines  already  referred  to,  and  tlie  defence  then  ol)tainod 
appears  to  be  formidable,  and  likely  to  be  resorted  to,  especially  with 
ground  mines  and  detached  circuit-closers. 

Ground  Mines  Fired  by  Observation.  —  (Ground  mines  which  are  fired 


Observation  Mines.  79 

by  observation,  i.e.,  by  an  observer  (or  by  two  obsei'vei-s)  from  a  dis- 
tance, when  the  vessel  attacked  is  seen  to  be  near  enough  to  the  mine, 
should  evidently  have  a  horizontal  circle  of  effect  sufficiently  large  for 
the  proper  working  of  the  observation  instruments,  and  this  will 
depend  upon  the  distance  separating  the  mines  and  the  instruments  and 
upon  the  accuracy  of  the  latter.  Assume  that  the  mines  are  about  one 
sea  mile  from  the  instruments  and  that  an  effective  horizontal  circle  of 
30  ft.  radius  is  desired.  Also,  assume  that  the  depth  of  water  is  60  ft., 
that  the  draught  of  an  ironclad  is  27  ft.,  and  that  the  shape  of  her  side 
is  somewhat  as  shown  in  Fig.  39.  A  geometrical  construction  will  then 
show  that  the  actual  distance  between  the  mine  and  the  nearest 
point  of  the  vessel  is   52  ft.     If  the  mines   were  situated  only  half 


VMVA'MMW^^>'&,i>/,. 


a  mile  from  the  observing  insti'uments,  equal  accuracy  would  be 
obtained  with  mines  having  a  horizontal  circle  of  effect  of  half  the 
former  dimensions,  and  the  striking  distance  is  then  reduced  to  43  ft., 
and  the  charges  can  be  reduced  in  nearly  the  same  proportion,  or  about 
four-fifths  of  those  for  52  ft.  By  increasing  the  depth  showii  on  the 
sketch  it  will  be  found  by  measurement  that  the  following  Table 
gives  the  striking  distances  required  for  effective  horizontal  circles  of 
30  ft.  and  15  ft.  radius  respectively  when  the  vessel  draws  27  ft.  of 
water. 

Similarly,    if    the    depth   of    water  be   50  ft.,   instead   of  GO  ft.,   the 
striking  distance  for  mines  one  mile  off  should  be  about  42]  ft.,  and  for 


80  Submarine  Mining. 

mines  at  half  a  mile  the  striking  distance  should  be  al)Out  34.',  ft.,  and 
tlie  cliarges  may  be  regulated  accordingly. 
Table  XXIV. 


Striking  Distances 

in  Feet. 

Depth  ill 

Oiving  a  Circle 

Giving  a  Circle. 

Feet. 

30  ft.  Rafliiis 

15  ft.  Radius. 

40 

39 

26^ 

60 

42i 

34i 

60 

52 

43 

70 

60 

51 

80 

68 

60 

90 

76 

69 

100 

85 

78 

Again,  a  mine  which  is  effective  in  GO  ft.  of  water  at  half  a  mile  off 
shore  would  be  equally  effective  in  50  ft.  of  water  at  seven-eighths  of  a 
mile  off  shore.     And  so  the  changes  can  be  rung. 

In  the  defence  of  some  harbours  by  submarine  mines  a  considerable 
economy  can  be  made  by  keeping  these  matters  in  view,  but  it  is  usual 
to  sacrifice  such  economy  and  to  employ  one  description  of  ground 
mine  for  all  situations,  thus  avoiding  numerous  patterns. 

From  a  Table  given  in  a  previous  chapter  it  will  be  found  tliat  the 
minimum  charges  for  an  effective  strike  of  52  ft.,  should  be  484  lb. 
blasting  gelatine,  or  558  lb.  gelatine  dynamite,  or  687  lb.  gun-cotton 
or  dynamite  No.  1. 

It  is  not  prudent  to  rely  upon  observation  firing  at  greater  distances 
than  one  sea  mile,  the  smoke  of  an  engagement,  or  fog,  or  thick  weather 
having  to  be  reckoned  with  in  this  class  of  mine.  If  then  we  limit  the 
employment  of  ground  mines  to  water  not  exceeding  60  ft.  in  depth,  a 
case  which  will  hold  484  lb.  of  blasting  gelatine  would  appear  to  meet 
all  requirements.  But  this  explosive  is  45  per  cent,  heavier  than  gun- 
cotton,  and  the  same  case  would  therefore  hold  only  334  lb.  gun-cotton, 
the  striking  distance  of  which  against  an  ironclad  is  only  26  ft.,  barely 
sufficient  for  an  observation  ground  mine  half  a  mile  off  shore  in  40  ft. 
of  water,  and  insufficient  for  greater  depths  or  distances.  On  the  other 
hand  a  case  to  contain  500  lb.  of  gun-cotton  will  liold  725  lb.  of  blasting 
gelatine,  the  former  having  a  striking  distance  of  38  ft.  and  tlie  latter 
of  77  ft.  when  acting  against  a  modern  war  vessel.  If,  therefore,  it  be 
intended  to  use  either  or  both  of  these  explosiA'es  in  a  time  of  emergency, 
it  would  appear  that  a  convenient  arrangement  would  be  obtained  by 
having  two  patterns  for  ground  mines.  Adding  20  per  cent,  to  the 
above  figures,  so  as  to  be  on  the  safe  side,  the  one  should  be  made  large 
enough  to  hold  either  600  lb.  of  gun-cotton  or  870  lb.  of  blasting 
gelatine,  and  the  other  to  hold  600  lb.  of  blasting  gelatine  or  414  lb.  of 
gun-cotton.  As  the  slab  gun-cotton  presents  flat  surfaces  to  the  curve 
of  tlie   cylinder,   each   case  would    liold    a   little   more  of   the  blasting 


Charges  avd  Cases  for  Grouml  M'nies.  81 

gelatine  than  denoted  by  tlie  abo\-e  figures,  and  it  would  he  nearer  the 
truth  to  put  round  figures  as  shown  on  the  Table  to  follow. 

(N.B. — Although  blasting  gelatine  is  superior  to  dynamite  and 
gelatine  dynamite,  it  may  occur  that  these  explosives  will  be  used 
in  a  time  of  emergency,  and  the  cases  would  contain  about  the  same 
weights  of  them  as  of  blasting  gelatine.) 

This  Table  gives  a  useful  technica  memorin  for  the  charges  of  large 
mines,  viz.,  to  use  10  lb.  of  blasting  gelatine  per  foot  of  strike  required. 
Also  that  the  same  case  will  hold  two-thirds  as  much  gun-cotton  by 
weight  possessing  half  the  strike  in  feet.  By  a  diagram  similar  to  the 
one  given  it  can  be  shown  that  a  mine  with  a  strike  of  90  ft.  can  be 
used  in  105  ft.  of  water,  at  one  mile  from  an  observing  station,  an 
effective  horizontal  circle  of  30  ft.  radius  against  vessels  of  27  ft. 
draught  being  obtained. 

The  employment  of  blasting  gelatine  in  ground  mines  is  evidently 
extremely  advantageous  when  the  waters  are  deep,  and  it  would  appear 
that  the  rule  in  the  English  service  limiting  the  employment  of  ground 
mines  to  depths  of  60  ft.  or  thereabouts  would  be  improved  if  a  larger 
limit  (say,  90  ft.  or  100  ft.)  were  fixed  upon,  ground  mines  being 
simpler  than  buoyant  mines,  and  less  liable  to  derangement. 

Best  Shape  for  Ground  Alines. — As  a  ground  mine  may  be  heavy  the 
cheapest  form  of  case  is  a  cylinder,  and  Staffordshire  plate  may  be  used 
in  its  manufacture,  the  required  strength  being  obtained  by  making  the 
skin  of  a  good  thickness,  and  the  diameter  of  the  case  as  small  as  is 
practicable.  In  the  English  ser-vice  the  ground  mine  most  usually  em- 
ployed holds  500  lb.  of  gun-cotton.  It  is  described  and  illustrated  in 
Colonel  (now  General)  R.  H.  Stotherd's  book  as  a  cylindrical  iron  case 
\  in.  thick,  34  in.  side,  30  in.  in  diameter,  and  its  ends  are  dished  out 
with  a  radius  of  30  in.  No  important  alterations  have  been  made  in 
this  mine  case,  but  it  has  been  strengthened  internally  by  a  lining  made 
of  Portland  cement,  experience  having  shown  that  the  case  is  weak  when 
subjected  to  countermining.  New  cases  should,  however,  possess  the 
requisite  strength  from  their  thickness,  shape,  size,  and  method  of 
manufacture.  A  cylinder  having  an  internal  radius  of  1  ft.  1|  in.  is 
convenient  for  loading  with  the  English  slabs  of  compressed  gun-cotton, 
and  the  interior  should  be  a  true  and  smooth  cylinder,  a  longitudinal  butt 
joint  being  employed,  with  the  covering  strip  outside.  The  ends  should 
not  be  dished  outwards,  but  be  plane  surfaces,  or  dished  slightly  inwards, 
and  the  end  joints  should  project,  thus  affording  an  opportunity  for 
hydraulic  rivetting,  and  making  a  very  strong  job. 

With  an  internal  diameter  of  2  ft.  3i  in.,  each  layer  of  compressed 
gun-cotton   1|  in.    thick  will   contain    14  slabs  of  the  explosive  in   its 


82 


Submarine  Minivg. 


Englisli  form,  two  of  tliera  being  sawn  across  diagonally,  and  the  centre 
slabs  being  sawn  as  required  for  the  introductioii  of  the  priming  charge 
and  tiring  apparatus  (see  Fig.  40).  This  gives  about  35  lb.  per  layer, 
17  layers  for  the  600  lb.,  and  a  total  length  of  2  ft.  6  in. 

For  the  smaller  cylinder,  as  slab  gun-cotton  stows  well  in  a  circle 
1  ft.  9  in.  in  diameter  (see  Fig.  41),  that  dimension  will  be  chosen  for 
the  internal  diameter  of  the  case.  Each  layer  of  gun-cotton  will  then 
contain  8|  slabs,  20A  lb.  per  layer  If  in.  thick,  19?,  layers  for  400  lb., 
and  a  total  length  of  2  ft.  10  in. 


\^^i 


Case  I.,  therefore,  is  27.5  in.  in  diameter  and  30  in.  long  inside,  and 
Case  II.  is  21  in.  in  diameter  and  34  in.  long  ioside. 

In  loading  these  cases  witli  slab  gun-cotton  the  last  three  layers  must 
be  composed  of  quarter  slabs.  It  is  better  to  do  this  than  to  use  a 
larger  loading  hole,  as  the  size  and  weight  of  the  door  or  "moutii- 
piece "  should  be  made  as  small  as  possible,  because  weight  is  of  im- 
portance in  the  buoyant  mines,  and  the  apparatus  for  the  ground  and 
buoyant  observation  mines  should  be  interchangeable,  tiius  reducing 
the  number  of  patterns. 

What  thickness  of  iron  should  be  used  in  these  cases  to  make  them  as 
strong  as  a  3-ft.  sphere  of  ;|-in.  steel  1  Now  the  strength  of  a  sphere  is 
twice  that  of  a  tube  of  equal  diameter  (Rankine),  and  the  strength  of 
the  sphere  varies  as  the  stjuare  of  thickness  of  shell,  and  inversely  as  tlie 

square  of  tlic  diameter,   or  as     - 


Also  the  strength  of  tlie  sides  of   a 


tube  varies  as    -   (/  being  th 
Id 


>ngth). 


Cases  for  Ground  Mines. 
Consequently  : 


and  t  =  0.29  in. 


30x27.5    (36)- 
Similarly  foi-  the  smaller  case  : 

i^'    =  <i)'  and  t  =  0.3l  in. 
21x34     (36)3 

This  assumes  that  the  cases  are  made  of  the  best  and   toughest  steel. 

But  it  is  proposed  to  make  them  of  wrought  iron,  the  strength  of  which 

is  but  little  more  than  half  that  of  steel.     Hence  for  the  large  cylinder : 

t- =  2  (0.29)-,  and  «  =  0.41  in.  of  iron. 

And  for  the  smaller  cylinder  : 

<-  =  2(0.31)-,  and  t^O.U  in.  of  iron. 

The  flat  ends  of  each  cylinder  should  be  made  slightly  thicker,  say  ?,  in. 

thick.     There  can  be  no  objection  on  the  score  of  weight  in  making  the 

whole  of  each  case  of  ^-in.  iron,  and  it  would  be  advantageous  to  do  so. 

The   projecting  joints  between  the  ends   and   sides  will    make   the 

cylinders  about  5  in.  or  6  in.  longer,  and  the  weights,   (fee,    are  shown 

in  the  following  Table,  which  also  gives  other  useful  information  : 

Table  XXV. — Cylindrical  Cases  for  Ground  Mines. 

Description. 
Material :  ;^-iu.  Staffordshire  iron  plate. 
Length  of  cylinder,  inside 

,,       ,,     case  over  all 

Diameter,  inside         

Side  surface  of  case,  including  strip  for  butt  joint 

End  surfaces  with  turnover...  

Weight  of  case  empty  in  air 

,,       ,,     salt  water  displaced 

,,       ,,     charge  blasting  gelatine  (dynamite  or  gelatine 
dynamite) 
Weight  of  cliarge  gun-cotton  slabs 

Effective  Strike  to  a  Man-of-War. 

When  loaded  with  blast  gelatine        . .  

,,  ,,  ,,      gelatine  dynamite  

,,  ,,  ,,      dynamite    ... 

,,  ,,  ,,      gun-cotton  slabs 

The  loading  hole  should  be  6  J  in.  in  diameter  if  English  pattern  gun- 
cotton  slabs  are  to  be  used.  Lugs  for  attachment  chains  should  not  be 
rivetted  to  the  case  by  palms,  as  it  is  difficult  to  keep  them  water-tight. 
If  the  method  of  constructing  the  cylinders  now  proposed  be  followed, 
it  would  be  easy  to  weld  projections  or  ears  on  the  turnover  of  flat  end 
pieces,  and  to  provide  each  ear  Avith  a  ring. 

In  order  to  prevent    a   cylindrical  case   from    rolling  about  on    the 


Larse 

Case. 

Small 
Case. 

30    in. 

34  in. 

36    ,, 

40  ,, 

27^^  „ 

21  ,, 

23  sq.ft. 

20  sq.ft. 

11.2  „ 

7.1   ,, 

6S4  lb. 

5401b. 

710  ,, 

480  ,, 

900  ,, 

600  „ 

000  „ 

400  „ 

90  ft. 

60  ft. 

78  „ 

52  „ 

67  „ 

45,, 

45,, 

30  „ 

s+ 


Sahmnrhi e  Mining. 


l)ottom  wlien  laid,  and  thus  not  only  getting  out  of  position,  but  in  all 
probability  damaging  the  electric  cable  at  its  point  of  attachment,  it  is 
necessary  to  tix  some  sort  of  cradle,  or  lash  two  short  spars  to  the  case, 
one  on  either  side  of  it,  thus  forming  a  rough  but  efficient  cradle. 

The  foregoing  descriptions  have  been  given  so  much  in  detail,  that  it 
will  be  unnecessary  to  show  any  drawings  of  these  mine  cases. 

Large  Buoyant  Mines. — When  very  deep  waters  have  to  be  mined 
with  large  charges,  it  is  necessary  to  employ  buoyant  cases,  and  most  of 
the  observations  which  have  already  been  made  on  small  contact  mines 
are  equally  applicable  to  large  buoyant  mines.  It  will  be  desirable  in 
the  first  place,  therefore,  to  settle  upon  an  effective  minimum  for  the 
charge  to  be  employed.  The  explosive  employed  should  certainly  be 
the  most  powerful  obtainable. 

Submersion. — Assuming  that  the  mines  are  buoyed  up  to  a  submer- 
sion of  40  ft.  (see  Fig.  42)  at  low-Avater  springs,  and  that   the   rise  and 


Diagram    showing   large   buoyant 
moored  Fcr  Firing  by  observoiiion  I 


lasting  Gelatine 

I    smallest  eFFective 


fall  of  tide  amounts  to  20  ft.,  the  mines  would  sometimes  be  submerged 
60  ft.,  and  should  therefore  possess  an  effective  striking  distance  of 
52  ft.  if  moored  a  mile  from  the  o])ser\ing  station,  and  of  43  ft.  if 
moored  half  a  mile  oil".  If  the  rise  and  fall  of  tide  were  less  than  20  ft. 
the  submersion  at  low  water  may  be  increased  by  the  difference.  Thus 
if  it  were  12  ft.  rise  and  fall,  the  submersion  may  be  48  ft.  at  low  water. 
The  maximum  striking  distance  of  52  ft.  would  thus  remain  unaltered. 

Charge  required. — A  charge  of  485  lb.  of  blasting  gelatine  possesses 
the  requisite  power,  as  also  does  a  charge  of  687  lb.  of  gun-cotton,  but 
the  former  is  much  to  be  preferred,  because  a  smaller  buoyant  body  is 
required  to  support  it,  and  this  is  important.  Moreover,  the  matter  of 
cost  is  considerably  in  favour  of  the  more  powerful  explosive  ;  500  lb.  of 
blasting  gelatine  will  therefore  be  selected  as  the  normal  charge  for  a 
large  buoyant  mine. 


Cases  for  Large  Buoyant  Mines.  85 

An  objection  has  been  urged  in  these  pages  against  the  use  of  an  air 
space  round  the  small  charges  for  contact  torpedoes,  but  the  same  argu- 
ments do  not  apply  to  large  charges  acting  at  a  much  greater  distance 
when  the  blow  delivered  is  of  a  racking  rather  than  of  a  punching 
character.  The  charge  may  therefore  be  held  in  the  buoyant  case,  and 
the  shape  of  this  case  should  be  spherical  for  the  reasons  already  given 
when  discussing  contact  mines.  The  buoyancy  is  then  a  maximum  for 
a  given  weight  of  case,  and  the  resistance  oftered  to  the  current  is  a 
minimum.  The  double  mooring  previously  advocated  for  contact  mines 
is  still  more  essential  for  observation  mines,  accuracy  of  position  being 
so  important.  Proceeding  as  in  the  last  example  for  contact  mines  to 
calculate  the  necessary  size  of  case  we  find  that 

14B-UP-7P'  =  0, 
where  B  is  the  availaljle  buoyancy  in  pounds  of  the  mine  when  loaded 
and  moored,  P  is  the  side  pressure  in  pounds  due  to  the  current  acting 
on  the  mine,  and  P'  is  the  side  pressure  on   the  wire  rope  and  cable, 
span  being  90  deg.,  and  the  mine  14  fathoms  above  the  bottom. 

Now  P=  1.03  V- A, 

A  being  the  diametric  area  of  the  sphere, 

And  F=2.85V-A\ 

A^  being  the  area  of  the  diametric  planes  of   the   cable   and   wire   rope 
resolved  into  the  vertical. 


-  -    -  cos  4.J  4  20  X  6 
10x12 


Substituting 


B=  1.03  V-  A  +  i  (2.85  V-  x  1 1 ) 
=  V^  (1.03  A+ 15.67) 
When  V  =  2  knots  per  horn-, 

B  =  4.12  A  +  62.6S. 
When  V  =  3  knots  per  hour, 

B  =  9.27  A+ 141.13. 
When  V  =  4  knots  per  hour, 

B=  16.48  A +  250.72. 
When  V  =  5  knots  per  hour, 

B  =  25.75  A  +  391.75. 

But  the  mine  has  to  support  500  lb.  of  blasting  gelatine,  57  lb.  of 
cable,  and  68  lb  of  wire  rope,  or  625  lb.  in  all,  in  addition  to  its  own 
weight.     Hence  the  buoyancy  when  empty 


=   4.12  A  4 

688  for 

■  2 

knots. 

=   9.27  A  + 

766  ,, 

3 

=  16.48  A  + 

876  „ 

4 

=  25.75  A  f 

1017  „ 

5 

,, 

86  Sxibviarine  Min'nvj. 

Size  of  Cases  for  Large  Buoyant  Mines. — Referring  to  Table  XX.  for 

steel  spheres  with  a  thickness  of  skin  =         ,  it  will  be  found  that  these 

144 

equations  are  satisfied  wiien  D,   tlie  diameter  of  the  case,  is  3.2  ft.  for 

a   2-knot  tide,   3.4  ft.   for  3  knots,   3.6  ft.  for  4   knots,   and   3.8;")   ft. 

for  5  knots. 

The  tidal  currents  most  usually  met  with  on  harbour  mine  fields  do 
not  exceed  2  knots  per  hour ;  a  42-in  spherical  case  of  Jj-in.  steel, 
which  is  effective  in  waters  up  to  3|  knots  per  liour,  will  therefore  answer 
well  in  mo.st  situations.  When  the  limit  of  3^-  knots  is  exceeded  the 
case  employed  should  be  a  4-ft.  spliere  of  .Vin.  steel,  which  is  efi'ective 
in  currents  up  to  5i  knots,  the  angle  of  span  and  the  method  of  moor- 
ing the  mines  hereinbefore  suggested  being  followed. 

Inasmuch  as  these  mines  must  be  loaded  with  blasting  gelatine,  and 
that  it  would  be  difficult  to  insert  the  apparatus  for  firing  the  charge 
into  the  bottom  of  the  mine  after  such  a  charge  has  been  inserted,  it 
will  be  advisable  to  provide  a  loading  hole  in  the  top  of  the  case,  in 
addition  to  the  hole  usually  made  in  the  bottom  for  the  apparatus.  The 
charge  can  then  be  inserted  after  the  apparatus,  and  can  be  packed 
closely  round  its  envelope  ;  also,  tlie  top  surface  of  the  explosive  can  be 
covered  with  a  light  deck  of  thin  wood,  kept  in  position  by  suitable 
battens  and  struts. 

The  writer  recommends  that  the  mines  be  attached  to  their  mooring 
lines  by  an  encircling  ring  made  of  wire  rope  of  smaller  diameter  than 
the  case,  such  ring  being  provided  with  thimbles  rove  into  it,  and  the 
ring  kept  in  place  by  means  of  a  second  and  similar  ring  and  braces  of 
wire  rope  between  them — as  was  recommended  for  the  spherical  buoys 
employed  in  connection  with  contact  mines.  In  this  manner  the 
employment  of  ears  or  palms  rivetted  to  the  case  is  avoided. 

The  following  Table  of  the  principal  details  of  the  two  buoyant  mine 
cases  which  it  is  proposed  to  adopt  will  be  useful  for  reference  : 

Table  XXVI. — Spherical  Cases  for  Buoyant  Mines. 


Description. 

Large 
Case. 

Small 
Case. 

Material :  Landore  steel,  diameter- 144  thickness. 

Diameter  of  sphere  inside 

48  in. 

42  in. 

Surface  of  sphere        

...    50.4  sq.ft. 

37.7  sq.ft. 

Weight  of  case  empty  in  air            

...       6721b. 

4401b. 

,,      salt  water  displaced       

..      2144  „ 

1427  „ 

,,       ,,      charge  (blasting  gelatine  preferred)  ... 

...       500  „ 

500  ., 

,,       ,,      apparatus 

30  „ 

30  „ 

,,      wire  rope  at  45  deg.  per  fathom  deep 

...       4.9  „ 

4.9  ,, 

,,      cable  at  45  deg.  per  fathom  deep 

...       4.1   „ 

4.1  ,. 

Area  of  diametric  plane        

...    12.57  sq.  ft 

.  9. 6 sq.ft. 

Spacbuj  fur  Large  Mines.  ^7 

Effective  Strike  to  a  Man,-o/-War. 

_        .   ..  Large  Small 

Description.  Case.  Case. 

When  loaded  with  blasting  gelatine       54  ft.  54  ft. 

,,         ,,         ,,        gelatine  dynaniit-  .                                             47,,  47,, 

,,         ,,         ,,        dynamite       ...  .           ..                                 -iS  ,,  38,, 

,,         ,,         ,,        gun-cotton  slabs  .  .           ..                                 38,,  38,, 

The  large  mines  recornineiided  sliould  tlierefore  lie  .spaced  as  follows  : 

Table  XXVII.— Spacinu  for  Large  Mines. 

At  or  over 

Buoyant,  large  and  small  sizes,  500  lb.  blasting  gelatine  ...  456  ft. 

,,  ,,        ,,        .,         ,»  I)      gun-cotton         ...         ...  321  ,, 

Ground,       ,,      si/.e,  900  lb.  blasting  gelatine      387,. 

,,     600  ,,    gun-cotton 184  ,, 

small      ,,     600,,    blasting  gelatine      228,, 

,,  ,,         ,,     400  ,,    gun-cotton 


91 


Before  leaving  the  cases  for  submarine  mines,  a  few  words  are 
desirable  on  the  distance  that  should  separate  the  large  observation 
mines.  Of  the  four  considerations  bearing  upon  this  point  with  respect 
to  contact  mines,  only  one  applies  to  the  observation  mines,  viz.,  that 
they  shall  be  spaced  at  such  minimum  intervals  that  the  explosion  of  one 
mine  cannot  injure  its  neighbours.  Assuming  that  the  apparatus  used 
in  the  mines  is  strong  enough  to  stand  any  shock  that  will  not  injure 
the  cases  themselves  (and  care  should  be  taken  that  this  is  so,  a 
care  that  is  too  frequently  neglected),  it  only  remains  to  calculate 
the  distances  at  which  the  charges  proposed  to  be  employed  will 
damage  the  cases  described.  The  buoyant  cases,  large  and  small, 
are  designed  to  be  equal  in  strength  to  a  3-ft.  steel  sphere  J  in.  thick, 
which  will  withstand  a  collapsing  pressure  of  1400  lb.  on  the  square 
inch  (see  top  of  page  59).  Now  500  lb.  of  blasting  gelatine  will 
produce  this  pressure  in  water  at  a  distance  of  about  456  ft.,  vide 
formula,  page  36,  and  500  lb.  of  gun-cotton  will  do  the  same  at  321  ft. 
Buoyant  mines  of  the  patterns  recommended  should  consequently 
be  moored  at  intervals  not  smaller  than  the  above,  according  to  the 
explosive  employed  in  them.  With  regard  to  the  ground  mines,  it 
can  be  shown  by  the  same  formulre  that  the  large  iron  case  can 
resist  a  collapsing  pressure  of  2931  lb.  on  square  inch,  and  the 
smaller  case  one  of  3364  lb.  Also,  that  900  lb.  of  blasting  gelatine  will 
produce  the  former  eflfect  at  387  ft.,  and  600  lb.  of  gun-cotton  at 
184  ft.  Also,  that  600  lb.  of  blasting  gelatine  will  produce  the  latter 
effect  at  228  ft.,  and  400  lb.  of  gun-cotton  at  91  ft. 

Conclusion. — The  various  descriptions  of  mines  under  control  and  of 
buoys  for  circuit-closers  have   now   been   examined   as  to   shape,    size, 


yS  Submarine  Mini  ay. 

weight,    displacement,   thickness,     nature    of     material,     resistance    to 
currents,  spacing,  itc. 

Messrs.  Day,  Summers,  and  Co.,  of  the  Nortliam  Iron  Works,  South- 
ampton, have  undertaken  to  manufacture  them,  and  any  additional 
information  can  be  obtained  on  application  to  this  firm.  The  methods 
of  mooring  them  have  been  roughly  indicated,  and  will  now  be  examined 
more  in  detail,  the  considerations  and  diagrams  which  should  settle 
many  matters  connected  therewith  being  fresh  in  the  mind  of  the 
reader. 


CHAPTER  Vll. 
Mooring  Gear  for  Submarine  Mine. 
Sinkers. — As  already  stated,  ground  mines  when  made  of  thick  iron 
are  sufficiently  heavy  to  keep  their  position  as  laid,  without  providing 
sinkers  for  them,  as  was  customary  a  few  years  ago,  the  development  of 
countermining  showing  that  it  was  a  better  arrangement  to  place  weight 
in  the  case  than  in  a  sinker  outside  the  case.  In  this  way  ground  mines 
can  be  made  much  stronger  than  they  used  to  be,  and  yet  be  handled 
and  moored  with  equal  facility.  Mooring  sinkers  for  ground  mines  are 
therefore  no  longer  required,  but  mines  which  are  buoyed  up  from  the 
bottom  (whether  they  be  contact  mines  or  mines  hred  by  detached 
circuit-closers  or  large  mines  fired  by  oliservation)  must  evidently  be 
anchored  to  the  bottom  in  such  a  manner  that  there  is  no  probability  of 
their  movhig  from  the  positions  in  which  they  are  laid.  Ordinary 
anchors  have  seldom,  if  ever,  been  employed  for  this  work,  because 
mines  are  generally  moored  by  single  moorings,  for  which  ^purpose  an 
anchor  is  unsuitable.  When  double  moorings  are  used  anchors  may  be 
employed,  but  it  is  more  difficult  to  place  them  exactly  in  position  than 
dead-weiglit  sinkers,  and  even  if  the  top  fluke  be  turned  down  they  are 
more  likely  to  be  fouled  and  dragged  out  of  position  afterwards.  More- 
over, on  hard  bottoms  they  are  more  liable  to  shift  their  positions  under 
normal  conditions  than  would  sinkers  of  suitable  weights.  If,  however, 
sinkers  were  not  procurable  in  sufficient  numbers  on  an  emergency,  it 
should  be  remembered  that  single-fluke  anchors  can  be  used  instead  for 
all  mines,  &c.,  moored  on  a  span. 

The  necessary  weights  of  sinkers  for  diB'erent  circumstances  have 
never  received  the  attention  which  the  subject  deserved.  Rules  of 
thumb,  founded  on  indifl'erent  theory  or  none  at  all,  were  followed  in 
the  early  stages  of  submarine  mining,  and  were  perpetuated  because  the 
time  and  attention  of  adepts  have  been  occupied  by  what  were  apparently 
more  important  matters. 

It  is,  however,  a  serious  thing  when  mines  walk  about  with  their 
sinkers,    and    take  up   new  positions  whicli   they  are   not   intended  to 


90 


Submarine  Mining. 


occupy ;  and  a  little  theory  (although  "  a  dangerous  thing ")  may, 
perhaps  with  advantage,  be  brought  to  bear  upon  this  simple  subject. 

In  order  to  ai-rive  approximately  at  the  necessary  weights  of  sinkers 
for  submarine  mines,  we  must  lirst  fix  upon  a  minimum  coefficient  of 
friction  between  a  sinker  and  the  bottom  of  the  sea.  The  "  R.E. 
Aide  Memoire,"  vol.  i.,  sec.  73,  states  :  "  To  move  a  stone  along  a  rough 
chiselled  floor  requires  |  of  its  weight."  In  other  words,  the  coefficient 
of  friction,  under  these  circumstances,  is  |.  But  a  sinker  should  be 
provided  with  projecting  feet  or  claws  which  carry  the  whole  weight  on 
a  few  points,  and  as  the  weight  is  always  sufficient  to  make  the  claws 
cut  into  such  a  surface  as  a  chiselled  stone  floor,  it  is  certain  that  even 
in  the  unfavourable  and  rare  occurrence  of  the  sea  bottom  being  flat 
rock,  the  coefficient  of  friction  would  be  something  in  excess  of  f .  In 
most  situations  the  bottom  yields  to  the  weight  of  the  sinker,  which  thus 
becomes  imbedded ;  and  when  this  occurs  the  subsequent  resistance  to 
horizontal  motion  must  be  greatly  increased.  Assuming,  however,  that 
the  minimum  coefficient  of  friction  between  a  sinker  and  the  sea  bottom 
is  2,  and  this  is  certainly  erring  on  the  safe  side  of  the  truth,  a  few 
calculations  will  give  the  necessary  weight  of  sinkers  for  contact  and 
other  buoyant  mines. 

Firstly,  let  us  find  the  weight  W  of  a  sinker  required  to  moor  a 
spherical  buoyant  body  possessing  an  available  Iraoyancy  B  lb.,  a 
diameter  D  ft.,  and  a  diametric  area  A  sq.  ft.,  in  a  current  of  V  knots 


Fm.4S. 


per  hour,  the  size  of  the  mine  and  the  weights  carried  bring  such  that 
the  deflection  of  the  system  from  the  vertical  is  a. 

Also  let  A'  represent  the  diametric  area  of  the  cross-section  of  mooring 
line  and  electric  cable  (or  of  the  electric  cable  alone,  if  the  body  be 
moored  by  tlie  cable). 

Tlion,    if  P   be   the   side  pressure  produced    by   tlie   current    on   the 


Weights  of  Sinkers.  91 

buoyant  body,  and  if  P'  be  the  side  pressure  on  tlie  mooring  line  and 
cable,  P=  1.03  V-A,  and  P  =  2.85  V=A>  (Froudc). 

For  simplicity  let  P'  be  transferred  so  that  its  theoretical  point  of 

pi 
application  is  at  the  mine,  the  same  result  being  obtained  when    „-  is  so 

applied. 

Then  ^     /'p^P'\      f 

B=I   P  +  -Q  I  cot  a 

=:V- cot  a  (1.03  A +  1.42  A'). 
But  W  -  B  =  the  weight  of  smker  on  the  bottom, 

•  ■-  s  ( W  -  B)  =  the  horizontal  force  required  to  move  it, 
Pi 
and  this  should  be  >  P  +  .,   by  an  amount  sufficient  to  withstand  any 

additional  strain  which  may  be  put  upon  the  .system. 

During  the  mooring  operations  it  is  often  necessary  that  a  large  boat 
shall  hang  on  to  the  mine,  and  tlie  resistance  so  offered  to  the  current 
must  be  allowed  for,  and  will,  moreover,  provide  a  margin  of  safety  as 
regards  the  weight  of  the  sinker.  Assume  that  the  resistance  added 
by  the  boat  so  moored  is  equivalent  to  that  of  a  totally  submerged 
sphere  with  a  diametric  area  of  1 0  square  feet  (it  would  be  a  large  boat 
to  offer  such  a  resistance)  the  equation  for  weight  of  sinker  then 
becomes 

3  (W-B)  =  V-  cot  ff  (1.03  A+1.42  A'+IO). 

The  same  formula  is  applicable  to  a  mine  moored  on  a  span  with  two 
sinkers,  for  if  the  weights  be  so  adjusted  that  the  down-stream  line 
is  just  slack  when  the  current  is  running  its  strongest,  the  result 
obtained  from  the  equation  will  be  correct ;  and  if  the  buoyancy  of  the 
mine  be  greater  than  necessary,  neither  line  will  ever  be  slack,  some  of 
the  buoyancy  being  supported  by  the  down-stream  sinker.  If  therefore 
the  equation  be  applied  to  find  the  weight  required  for  the  up-stream 
sinker  and  the  buoyancy  held  down  by  the  other  stream  sinker  be 
neglected,  the  result  must  evidently  be  on  the  safe  side  of  the  truth.  If 
the  tide  run  with  equal  velocity  in  the  other  direction,  and  if  the  angle 
a  for  each  mooring  line  be  approximately  the  same,  the  sinkers  should 
be  of  equal  weight. 

Let  us  apply  the  formula  to  find  W  of  each  of  the  two  sinkers  used 
with  a  42-in.  spherical  mine,  containing  a  charge  of  500  lb.,  and 
supporting  125  lb.  of  cable  and  mooring  line  in  21  fathom.s,  the  whole 
arranged  as  previously  described  and  illustrated  ;  then  the  current 
velocity  being  2  knots  per  hour, 

B  =  987* -625  =  362  lb. 
a  =  45  deg.,  A  =  9.6,  Ai  =  ll,  V  =  2, 

*  See  Table  XX. 


92  Submarine  Mining. 

and 

W  =  362  +  f  x4(9.9  +  15.6-)  10). 
=  575  lb.  in  salt  water. 
=  671  lb.,  say  6  cwt.,  in  air. 
Similarly  for  a  2^-knot  current, 

W  =  362  +  fx  6.25x35.6, 
=  696  lb.  in  salt  water, 
=  811  ,,    say  7i  cwt.,  in  air, 
and 

W  =  9S1   ,,     ,,     8f     ,,     for  a  3-knot  tide, 
and 

=  1183,,     „     10^  ,,         „  ^ 

Applying  the  formula  to  the  large  48-in.  buoyant  spherical  mine  in 
the  same  depth  of  water,  but  in  currents  ranging  from  4  knots  to 
5|-  knots,  we  have:  A  =  12.57,  B  =  1472  -  625  =  847,  and  the  rest 
as  before.     Then  for  a  4-kiiot  current, 

W  =  847  +  i:x  16  (12.95+ 15.6+ 10). 
=  1771  lb.  in  salt  water. 
=  2066  „    say  IS  cwt.,  for  4  knots. 
Similarly, 

W  =  2354  lb.,  say  21  cwt.,  for  44  knots. 
=  2673       „       24         .,         5 
=  3028       ,,       27         ,,        5i      ,, 

These  heavy  weights  speak  forcibly  against  the  employment  of 
buoyant  mines  of  any  description  in  swift  currents,  if  such  can  by  any 
possibility  be  avoided.  Not  only  must  the  gear  be  heavy,  but  the  con- 
tinued strains  and  chafing  are  apt  to  damage  the  insulation  of  tlie 
electi'ic  cables  and  do  other  mischief. 

Applying  the  Formula  to  Electro-Contact  Mines,  we  find  that  tlic  values 
for  W  come  out  thus  : 

When  a  spherical  mine  3.25  ft.  in  diameter  is  loaded,  primed,  and 
moored  in  the  service  manner  in  water  11  fathoms  deep,  running 
4  knots,  its  maximum  efficiency  is  obtained  when  «  =  24  deg.  (see 
example  on  foot  of  page  61) ;  also  B  =  6.30  lb.,  A  =  8.3  square  feet,  A'  =  7 
square  feet.     Tlien  by  formula 

W  =  630+  *  X  4  X  4  X  2.25  (1.03  x  8.3  +  1.42  x  7  +  10). 
=  2169  lb.  in  salt  water. 
=  253011b.  in  air. 
=  22i  cwt. 
Similarly,    if  the    same    mine    be   moored    in    the   same    water,    l)ut 
velocity  of  current  =  3  knots, 

W=   630+1x3x3x2.25x28.5. 
=  1045  lb.  in  salt  water. 
=  1219  lb.  in  air. 
=  11  cwt. 


Weights  of  Sinkers.  93 

Again,  if  this  mine  be  moored  in  21  fathoms  it  is  efficient  in  a  current 
of  a  little  over  2  knots,  as  shown  previously.  15  is  reduced  by  50  lb.,  the 
weight  of  additional  cable  and  wire  rope ;  A'  is  increased  by  7  square 
feet  for  same  reason,  and  a  is  reduced  to  18  deg.  (whose  cot  =  3.08)  for 
reasons  already  given  on  page  61. 

.-.  \V  =  580  +  fx2x2x3.08  (28.5  +  7). 
=  1290  lb.  in  salt  water. 
=  140.5  lb.  in  air. 
=  12|cwt. 
Turning  to   tlie  examples  given  of  a  contact  Ijuoy*  (and  small  sus- 
pended mine)  on  two   sinkers  we  find   that  in   21    fathoms  the  dead- 
weight supported  by  the  buoy  =  about  1501b.,  and  if  V  = -i  knots  a  3-ft. 
sphere  of  steel  j  in.  thick  possessing  a  buoyancy  empty  of  aVjout  620  lb. 
is  required  and  the  weight  of  sinker. 

W  =  470  +  ^  X  4x4  (l.O.S  X  7.06  +  10..'}  x  0..j  +  1.42  ;:  1:1.4  +  10). 
=  1,352  in  salt  water. 
=  1577  in  air. 
=  14  cwt. 
Similarly  in  21  fathoms  and  3^  knots, 
W  =  470  +  fx  Six  Six  36.8. 
=  1146  in  salt  water. 
=  1337  in  air. 
=  12  cwt. 
Xow  it  was  shown  that  a  2.',-ft.   sphere  would   do  for   3  knots  with 
other  conditions  as  above. 

.  •.  \V  =  290+  =  X  3  X  3  (1.03  +  4.9  +  1.03  x  0.5+1.42  x  13.4  +  10). 
=  757  in  salt  water. 
=  883  in  air. 
=  8  cwt. 
Similarly  in  a  2-knot  tide, 

W  =  290  +  fx2x  2x34.6. 
=  497  in  salt  water. 
=  580  in  air. 
=  5Jcwt. 
Again,  in  1 1  fathoms  and  3J  knots  and  the  same  sphere, 
W  =  340  +  |  X  3  X  3   (1.03  X  4.9  ^- 1.03  x  0.5+1.42  x  6.7  +  10). 
=  669  in  salt  water. 
=  780  in  air. 
=  7  cwt. 
The   weights    of  the  sinkers  shown  in   Table   on  next  page,    whicli 
would  be   required   in  tlie  majority  of  harbours,   are  from   6  cwt.   to 
lOi  cAvt.  for  the  buoyant  observation  mines,  and  from  5  cwt.  to  12  cwt. 
for  the  contact  mines. 

'  The  five  following  calculations  should  be  slightly  niodiliej  (see  footnote  to 
page  59),  but  the  results  would  not  be  materially  atl'ected  thereby. 


94 


Submarine  Mining. 


Table  XXVIII. ^Sinkers  for  Spherical  Mines,  &c. 

Found  by  Formula 

\V  =  B  +  iiV-  cot  a  (1.03  A  +  1.42  Ai  +  10). 


Description  of 
Case,  &o. 

1 

I1 

III 

a 
1 

1^ 

1"^ 

li 

II 

> 

it 

i-'- 

ill 
hi 

1 

ll 

if 

i 

i 

=  144i 

B. 

i     V. 

A. 

A\ 

a. 

w 

Buoyant       mine, 

ft. 

lb. 

deg. 

cwt. 

~hr 

large,     on     two 

sinkers 

4 

847 

21 

54 

12.57 

11 

45 

27 

625 

Ditto 

4 

847 

21 

5 

12.57 

11 

45 

24 

625 

Ditto 

4 

847 

21 

44 

12.57 

11 

45 

21 

625 

Ditto 

4 

847 

21 

4 

12.57 

11 

45 

18 

625 

Buoyant      mine. 

small,    on     two 

sinkers 

34 

362 

21 

34 

9.6 

11 

45 

104 

625 

Ditto 

H 

362 

21 

3 

9.6 

11 

45 

8| 

625 

Ditto 

H 

362 

21 

2i, 

9.6 

11 

45 

7i 

625 

Ditto 

3i 

362 

21 

2" 

9.6 

11 

45 

6 

625 

Contact  mines  on 

single  sinker   ... 

H 

630 

11 

4 

8.3 

7 

24 

224 

200 

Ditto 

H 

630 

11 

3 

8.3 

7 

24 

11 

200 

Ditto 

H 

580 

21 

2 

8.3 

14 

18 

124 

250 

Contact  mines  on 

two  sinkers      . . . 

3 

470 

21 

4 

7.06 

13.4 

45 

14 

150 

Ditto 

3 

470 

21 

34 

7.06 

13.4 

45 

12 

150 

Ditto 

24 

290 

21 

3 

4.9 

13.4 

45 

8 

150 

Ditto 

24 

290 

21 

2 

4.9 

13.4 

45 

5i 

150 

Ditto 

24 

290 

11 

34 

4.9 

6.7 

45 

100 

It  now  remains  to  settle  upon  the  best  shape  of  sinker.  A  convenient 
form  was  designed  by  the  writer  in  1875,  was  adopted  in  1878  by  the 
Government,  and  has  remained  the  service  pattern  up  to  date.  Prior 
to  1878  the  mushroom  sinkers  did  not  house  one  into  the  other,  and 
they  consequently  occupied  valuable  space  in  store,  or  encumbered  the 
ground  round  the  cranes,  or  sinker  platforms  had  to  be  built  whence 
they  could  be  rolled  on  to  the  trucks.  Moreover,  when  transported 
from  the  central  store  to  out  stations,  they  took  up  more  space  on  board 
ship  and  were  not  so  easily  secured  in  the  hold  as  at  present.  The  sinker 
is  circular,  and  all  between  6  cwt.  and  I  ton  can  be  made  of  the  same 
diameter,  viz.,  2  ft.  2  in.;  the  different  weights  being  obtained  by  dif- 
ferent heights.  It  has  a  flat  top  (see  Figs.  44  and  45)  and  a  strong 
central  3-in.  eye  made  of  |-in.  wrought  iron.  Near  the  circumference 
there  are  three  triangular  indentations,  about  3  j  in.  deep  at  the  outside 
and  narrow  part,  and  sloping  upwards  to  nothing  at  the  inner  and 
wider  portion. 


Pattern  of  Smkers. 


Each  indentation  is  provided  with  a  wrought-iron  bar  across  the  top 
of  the  outer  opening,  and  these  bars  not  only  strengthen  the  sides  of 
the  indentations,  but  act  as  additional  eyes  for  attaching  chains,  &c.,  to 
the  sinker,  as  required,  and  keep  the  feet  m  position  when  the  sinkers 
are  housed.  The  bottom  of  the  sinker  is  slightly  concave,  and  has  three 
feet  cast  upon  it  which  fit  into  the  three  indentations  on  the  top  of  a 
similar  sinker  below  it.  The  service  pattern  has  four  feet  and  four 
indentations  instead  of  three.  A  few  improvements  now  suggest  them- 
selves to  the  writer. 

1.  The  wrought  iron  should  be  |  in.  in  place  of  f  in. 

2.  It  would  often  be  convenient  to  connect  two  sinkers  rigidly  to 
form  a  single  sinker  of  greater  weight,  and  this  can  readily  be  provided 
for  by  simply  leaving  three  vertical  holes  (see  Fig.  44)  through  which 
wrought-iron  bolts  could  be  passed  and  secured  by  suital)le  nuts. 


Fui.  44. 


Fig.  45.   "*'•"' 

Secluirv  orv  A.  B. 

3.  As  the  system  of  mooring  by  the  electric  cable  has  been  advocated 
in  these  articles,  especially  when  two  sinkers  are  employed  on  a  span, 
provision  should  be  made  for  securing  the  cable  to  a  sinker  in  such  a 
manner  that  it  shall  be  firmly  held  at  the  centre  of  the  sinker.  When 
so  used  the  central  eye  will  not  be  required,  and  the  cable  can  therefore 
be  fixed  by  a  hook  passing  through  a  hole  from  the  central  cavity  in  the 
bottom  of  the  sinker,  the  nuts  being  put  on  by  a  box  spanner. 

Cast-iron  sinkers  of  above  pattern  26  in.  in  diameter  weigh  in  air 


96  Submarine  Mininfj. 

about  1331b.  per  inch  of  depth,  the  average  weight  of  cast  iron  being 
4441b.  per  cubic  foot.  They  can  be  cast  of  any  desired  thickness 
between  the  limits  of  5  in.  and  13^  in.,  which  give  weights  of  G  cwt. 
and  16  cwt.  respectively.  Beyond  tliese  limits  sinkers  of  smaller  or 
larger  diameter  should  be  employed,  a  good  rule  being  that  the  depth 
shall  range  from  about  one-fifth  to  half  the  diameter.  But  if  26-in. 
sinkers  be  cast  weighing  6  cwt.,  8  cwt.,  and  10  cwt.  in  air,  and  the 
suggestion  be  adopted  of  bolting  two  together  when  required,  we  obtain 
a  range  from  6  cwt.  to  20  cwt.  at  steps  of  2  cwt.     Thus  : 

6,8,  10,  (6 +  6)  =  12,  (6 +  8)  =  14,  (6+ 10),  or  (8  +  8)=  16, 
(8  +  10)  =  18,  and  (10+10)  =  -20. 
Such  a  range  would  probably  meet  all  the  usual  requirements  for  tlio 
service. 

If,  however,  it  be  considered  advisable  to  provide  for  the  range  with 
still  smaller  steps,  it  could  be  done  by  adopting  a  further  suggestion 
which  is  now  made,  viz.,  to  manufacture  the  sinkers  in  three  parts  :  top 
piece,  that  part  shown  above  the  dotted  line  0  D  in  Fig.  45  ;  bottom 
piece,  that  part  shown  below  0  D,  and  in  the  middle  a  number  of  iron 
discs  of  the  commonest  and  cheapest  ship-plate,  say  1  in.  thick,  the  discs 
being  added  or  subtracted  according  to  the  weight  of  sinker  required. 
When  20  cwt.  has  to  be  exceeded,  a  convenient  diameter  for  cast-iron 
sinkers  is  3  ft.,  and  this  gives  266  lb.  per  inch  of  depth,  or  double  the 
weight  of  the  26-in.  sinkers.  A  20-cwt.  sinker  must  then  be  8.4  in. 
thick  and  a  30-cwt.  sinker  12.6  in.  thick.  As,  however,  these  sinkers 
are  only  required  on  rare  occasions,  they  can  be  cast  when  required  of 
the  thickness  to  give  the  desired  weight,  and  special  patterns  need  not 
be  stored. 

It  is  seldom  necessary  or  desirable  to  moor  mines  on  sinkers  weigh- 
ing less  than  5  cwt.  in  air.  But  light  sinkers  are  required  for  marking 
buoys  and  other  purposes,  and  it  is  convenient  that  the  weight  should 
then  be  adjustable  between  the  limit  of  i  cwt.  and  2  cwt.  or  3  cwt. 
This  can  be  done  by  making  the  sinker  (now  suggested)  of  several  iron 
discs  and  bracing  them  together  by  through  bolts,  the  number  of  discs 

O)  (O) 


"W~^ 


Fig.  46—47. 
used  giving  the  required  weight.     Discs   16  in.  in  diameter  and  1  in. 
thick,  made  of  wrought  iron,  weigh  ^  cwt.  each,  and  these  dimensions 
are  recommended.     Two  or  more  eye-bolts  should  be  provided  (as  shown 
in  Fig.  46 — 47)  for  mooring  line,  slip  line,  Arc. 


Mooring  Lines.  97 

Mooring  Lines. — These  are  made  of  tlexiblu  steel  wire  ropo,  tlie 
desiderata  being  strength  united  as  far  as  possible  with  flexibility, 
lightness,  small  diameter  so  as  to  resist  moving  water  as  little  as 
possible,  and  lasting  power.  Strength  and  flexibility  are  obtained  by 
the  employment  of  steel  wires  of  small  gauge,  but  durability  in  salt 
water  is  obtained  best  by  wires  of  large  dimensions.  A  compromise  is 
therefore  necessary.  In  the  first  place  let  us  examine  the  working 
loads  which  may  be  brought  upon  such  ropes.  The  outside  limits  of 
weight  are  practically  given  in  the  column  marked  W  of  the  Table  of 
sinkers,  for  these  sinkers  in  many  instances  would  have  to  be  brought 
to  the  surface  again  by  means  of  the  wire  ropes  which  connect  the 
mines  to  them.  Thus  the  large  buoyant  mine,  Fig.  42  (page  84), 
say  in  21  fathoms,  the  current  running  5 J  knots,  must  have  27-cwt. 
sinkers,  and  if  they  become  imbedded  in  mud  50  per  cent,  additional 
tension  might  come  on  the  wire  rope  before  they  would  budge.  Thus 
the  tension  might  rise  to  as  mucli  as  50  cwt.,  say  2|-  tons,  and  the 
breaking  strain  of  such  rope  should  therefore  not  be  less  than  15  tons. 

Similarly,  the  smaller  size  of  500-lb.  buoyant  mines  when  moored  in 
21  fathoms,  and  a  current  velocity  of  3|  knots,  require  two  sinkers 
of  lOi  cwt.  each,  or  16  cwt.  as  the  safe  load  of  the  wire  rope,  say  a 
breaking  strength  of  nearly  5  tons.  Also,  the  3|-ft.  spherical  electro- 
contact  mines  in  1 1  fathoms  and  a  4-knot  current,  if  on  a  single  moor- 
ing, require  a  sinker  of  22|  cwt.,  and  therefore  a  mooring  line  up  to  a 
safe  load  of  nearly  34  cwt.,  say  a  breaking  strain  of  10  tons.  Also 
contact  mines  on  two  sinkers  in  21  fathoms,  and  4-knot  current, 
require  sinkers  of  14  cwt.,  and  therefore  a  mooring  line  up  to  21  cwt., 
or  a  breaking  strength  of  nearly  6|  tons.  But  the  large  spherical 
mines  on  a  single  mooring  are  not  recommended;  and  the  large 
500-lb.  buoyant  mines  in  deep  and  swift  waters  should  only  be  rarely 
employed.  For  most  situations,  therefore,  a  breaking  strength  of 
6A  tons  is  ample,  and  frequently  one  of  5^-  tons  is  suflicient.  A  2-in. 
steel  wire  rope  may  therefore  be  taken  and  accepted  as  strong  enough 
for  submarine  buoyant  mines  in  general,  and  2|  steel  wire  rope  for  the 
exceptional  situations  mentioned.  The  Table  on  the  next  page  is  for 
Mr.  BuUivant's  patterns. 

The  information  given  in  the  last  column  is  important.  If  smaller 
drums  be  used,  the  wire  rope  is  sure  to  be  damaged,  and  the  diameter 
of  the  drums  on  the  steam  winches  of  the  mooring  steamers,  as  well  as 
those  of  the  hand  winches  on  the  pinnaces,  must  be  fashioned  accord- 
ingly, and  the  gearing  so  designed  that  the  winches  will  then  work 
properly  when  the  maximum  strain  is  put  on  the  wire  rope.  The 
larger  the  barrel  the  better,  so  far  as  the  rope  is  concerned,  but  care 
H 


Sulmia vine  Mining. 


must  be  taken  to  see  that  the  machinery  is  then  strong  enough  to  turn 
it  with  the  maximum  load  upon  it.  When  the  rope  only  passes  over  a 
sheave,  tiie  diameter  of  the  sheave  may  be  one-sixth  less  than  the 
dimensions  given.  The  ■2-in.  rope  is  very  convenient  for  submarine 
mining.  It  consists  of  six  strands  round  a  hempen  core,  each  strand 
containing  twelve  No.  19  B.W.G.  galvanised  steel  wires.  Its  circum- 
ference and  its  weight  are  a  little  less  than  the  figures  given  on  the 
Table,  and  its  strength  is  a  little  more.  With  a  proof  strain  of  about 
4  tons  it  stretches  about  1  in.  per  fathom.  This  rope  will  not  dete- 
riorate in  store  if  kept  well  oiled,  and  Mr.  Bullivant  informs  the  writer 
that  the  4|-in.  patent  flexible  steel  wire  rope  he  supplied  to  the  ship 
Lady  Jocelyn  in  September,  1874,  was,  after  it  had  been  in  use  ten 
years,  tested  at  Mr.  Kirkaldy's  public  testing  machine,  and  it  actually 
took  a  greater  breaking  strain  than  was  guaranteed  at  the  date  of 
supply. 
Table  XXIX. — Paeticulars  of  Wire  Ropes  for  Mooring  Lines. 


Weight  per  Fathom 

In  Air. 

In  Salt 
Water. 

in. 

lb. 

lb. 

3.0 

7.0 

6.1 

2.75 

5.5 

4.8 

2.5 

4.5 

3.9 

2.25 

3.75 

3.3 

2.0 

2.75 

2.4 

1.75 

2.0 

1.75 

1.5 

1.75 

1.5 

1.25 

I.O 

0.9 

1.0 

0.75 

0.65 

Guaranteed 
Brealcing 
Strain. 


tons. 
18.0 
15.0 
12.0 
9.0 
7.0 
5.5 
4.0 


2.5 
1.75 


Diameter  of  Barrel 

or  Sheave  round 

REMARKS 

which  it  may  be 

Worked. 

in. 

18.0 

The    safe    load 

16.5 

should  not  ex- 

15.0 

ceed      i      the 

13.5 

breakingstrain. 

12.0 

10.5 

9.0 

7.5          \ 
6.0          J 

I  Useful  for  moor- 
-!    ing  the  niark- 
t   ing  buoys. 

It  not  unfrequently  occurs  that  mines  have  to  be  raised  and  the 
length  of  their  mooring  lines  altered  as  quickly  as  possible.  The 
following  arrangement  recently  designed  by  the  author  provides  for 
such  a  contingency.  The  top  of  the  mooring  line,  instead  of  terminat- 
ing as  usual  in  an  eye  to  be  shackled  to  the  ring  of  tiie  attachment 
chain  or  Miie  rope  sling  on  tlie  mine  case,  is  merely  cut  to  an  end  and 
served  or  crowned.  The  rope  is  then  fastened  to  the  ring  by  a  double 
turn,  and  the  end  clamped  to  the  standing  part  of  the  mooring  line  by 
a  mechanical  clip  formed  of  two  small  iron  plates  witli  grooves  across 
them  for  the  wire  rope,  a  central  bolt  and  nut  clamping  the  plates 
firmly  togetlier  after  the  rope  has  been  inserted. 

Chain. — When  a  buoyant  mine  has  to  be  raised  it  is  not  desirable 
to  use  the  aniiourod  electi-ic  ralile  for  this  purpo.sc,   althoui;]!  it  ouglit 


TrippliKj  Chains  and  Sliackh 


99 


to  be  strong  enough  if  required.  It  is  hcitci-  to  stopiuT  ;i  ])i(!ce  of 
chain  along  tlie  cable  of  sufficient  Icngtli  to  rcacli  from  (lie  sinlair  to 
the  surface,  and  thence  over  the  shea\e  or  Joggle  at  tlio  bow  of  the 
mooring  steamer  to  the  winch  or  capstan.  The  remarks  just  made 
concerning  the  necessary  strengths  of  wire;  mooring  ropes  apply  equally 
to  these  so-called  tripping  chains,  and  the  following  Table  may  be 
useful  : 

Table  XXX. — Particulars  of  Tripping  Chains. 


Chain  Cable, 

Weight  per  Fathom 

Breakin" 

Short-Linked 

Proof  Strain. 

Strain." 

Rkmarks. 

Size. 

In  Air 

In  Salt  Water. 

in. 

lb. 

lb. 

tons. 

tons. 

The  chain   should 

\l 

30 

25.0 

10.1 

15.1 

begalvanised.  The 

H 

25 

20.8 

8.5 

12.75 

width  of  each  link 

Tff 

21 

17.5 

7.0 

9.5 

should  be  §  of  its 

l\ 

17 

14.2 

5.5 

7.25 

length.    Thef-in., 

A 

14 

11.7 

4.5 

6.0 

^-in.,&T5-in.  chns. 

tV 

13.5 

11.3 

4.1 

5.5 

are     those     most 

tV 

10.35 

S.9 

3.75 

5.0 

usually  employed. 

Shackles. — Before  concluding  these  remarks  on  the  mooring  gear,  a 
few  words  are  necessary  concerning  a  small  detail  that  has  given  an 
infinity  of  trouble.  An  ordinary  shackle  with  a  split  pin  is  unsatis- 
factory, as  the  split  portion  becomes  rusty  and  frequently  breaks. 
Perhaps,  if  made  of  steel,  this  defect  may  be  rectified.  A  shackle  with 
a  screw  pin  is  apt  to  unscrew  and  become  unfastened  by  the  constant 
swaying  motion  of  a  buoyant  mine  in  a  current,  and  if  the  pin  be 
secured  through  its  eye  to  the  shackle  by  means  of  wire,  the  latter  is 
not  easily  disengaged  on  a  cold  day  by  a  man  hanging  over  the  bow 
of  a  mooring  steamer  with  only  one  hand  available.  When  picking  up 
mines  the  necessity  of  a  shackle  that  can  be  easily  unfastened  and  yet 
that  will  not  become  unfastened  unintentionally,  became  apparent. 

A  Scotch  smith,  M 'Inlay  by  name,  who  was  a  sapper  in  the  Royal 
Engineers,  invented  an  arrangement  which  answered  well.  He  secured 
and  incorporated  a  small  cross-pin  with  the  shackle  pin  so  that  half 
of  the  cross-pin  projected  beyond  the  surface  of  the  shoulder  of  the 
shackle  pin,  and  he  filed  an  indentation  in  the  corresponding  surface 
of  the  shackle,  so  that  when  the  shackle  pin  was  screwed  up,  the 
shackle  itself  was  pushed  back  or  bent  until  the  cross-pin  came  opposite 
the  indentation,  and  the  spring  of  the  shackle  then  caused  it  to  fly 
back,  making  the  whole  secure.  These  shackles  never  come  undone 
accidentally,  and  can  yet  be  unfastened  easily  by  a  small  marlinspike. 
Another  excellent  shackle  is  the  in\ention  and  has  been  patented  by 
Major  R.  M.  Ruck,  R.E.  In  this  arrangement  the  pin  is  secured  by 
II  2 


100  Submarine  Mining. 

means  of  an  india-rubber  washer,  which  engages  the  pin  over  a  portion 
that  is  reduced  in  diameter.  The  washer  keeps  the  phi  in  position 
when  there  is  no  strain  on  the  shackle,  but  when  the  shackle  is  in 
tension  a  small  catch  at  the  end  of  the  pin  prevents  it  from  slipping 
back.  To  open  the  shackle  there  must  be  no  tension  upon  it,  when  the 
pin  can  be  readily  forced  back  by  the  thumb,  and  then  pulled  at  the 
other  end  until  the  catch  is  brought  up  by  a  rubber  washer.  The 
shackle  is  closed  by  simply  pushing  the  pin  back.  This  sliackle  has 
recently  undergone  certain  reputed  improvements,  but  the  foregoing 
description  explains  the  idea  underlying  them,  and  if  further  informa- 
tion be  i-equired  it  can  be  obtained  by  writing  to  the  makers,  Messrs. 
Emerson,  Walker,  and  Thompson  Brothers,  Winlaton,  Blaydon-on- 
Tyne. 


101 


CHAPTER  VIII. 
Electric  Cables  for  Submarine  Mining  Purposes. 

General  Efmarks.—The  manufacture  of  electric  cables  for  submarine 
work  has  become  a  national  industry,  and  one  in  which  we  have  few 
competitors.  Some  of  our  foremost  electricians  are  intimately  con- 
nected with  the  great  commercial  companies  thus  evolved,  and  the 
matter  is  so  thoroughly  understood,  and  has  so  frequently  been  treated 
in  various  periodicals  and  pul)lications,  that  it  is  unnecessary  to  do 
more  than  indicate  the  requirements  of  submarine  mining,  and  any 
electric  cable  engineer  will  supply  all  the  additional  information  that 
may  be  required. 

Multiple  Cable  Cores. — In  order  to  obviate  the  necessity  of  employing 
a  large  number  of  cables  on  a  restricted  area,  it  is  desirable  to  employ 
multiple  cables,  and  to  lay  them  from  the  firing  stations  on  shore  to 
certain  convenient  points  selected  near  to  or  on  the  mine-fields,  to 
which  points  the  single  cables  of  the  mines  can  be  led  and  connected, 
each  to  one  of  the  cores  of  the  multiple.  The  disposition  of  the  mul- 
tiple cables  can  usually  be  so  arranged  that  they  need  not  cross  an 
anchorage,  and  many  of  them  can  then  be  laid  permanently,  ready  for 
war  purposes.  The  most  convenient  multiple  cables  for  employment 
in  submarine  mining  are  four-cored  and  seven-cored  ;  they  should  be 
armoured  for  the  sake  of  protection  and  strength  ;  and  there  is  no 
necessity  for  them  to  be  brought  round  any  small  drum  in  the  process 
of  recovery,  or  what  is  termed  "picking  up." 

Under  such  conditions  gutta-percha  is  the  best  dielectric,  and  is 
therefore  recommended  for  employment  in  the  multiple  cables  for 
submarine  mining,  care  being  taken  that  it  is  stored  in  water  from  the 
time  it  is  made  to  the  time  it  is  laid  ;  and,  consequently,  that  it  is 
taken  to  the  station  in  tanks,  and  never  exposed  to  the  direct  rays  of 
a  summer  sun  in  this  country,  or  of  a  tropical  sun  at  any  season. 

It  M^ill  be  seen,  therefore,  that  multiple  cables  can  be  treated  very 
similarly  to  the  present  deep-sea  telegraph  lines,  and  consequently  that 


102  Suhmiirine  Mining. 

tlieir  general  method  of  construction,  and  the  manner  in  whicli  they  are 
laid,  or  recovered,  may  assimilate  therewith. 

Sinyle  Cable  Cores. — It  is  impossible  to  deal  so  effectively  with  the 
single  cables. 

They  must  be  exposed  for  a  certain  period  during  the  process  of  con- 
necting up  the  mines,  cables,  chains,  wire  ropes,  sinkers,  itc,  on  shore, 
and  afterwards  in  the  mooring  operations.  Also  when  a  faulty  mine  is 
picked  up,  the  single  cable  is  again  exposed  during  a  repetition  of  these 
actions.  Moreover,  in  picking  up  mines  it  is  frequently  necessaiy  to 
take  considerable  strains  on  the  single  cables,  and  to  hoist  upon  them 
by  means  of  crabs  or  bollards  revolved  by  power.  Under  such  circum- 
stances, the  india-rubber  covered  core  known  as  Hooper's  is  better  than 
a  gutta-percha  covered  core.  This  core  can  be  stored  dry  on  the  drums 
as  received  from  the  makers,  if  a  cool  and  dark  place  be  available ;  but 
this  description  of  storage  for  any  great  length  of  time  is  not  so  trust- 
worthy as  wet  storage  in  cable  tanks  constructed  for  the  purpose  ;  or  in 
the  sea,  in  large  coils,  just  below  low-water  mark. 

Siihterra7iea7i  Cables  on  Sliore. — En  passant  it  may  be  remarked 
that  Hooper's  core  unarm  oured,  but  covered  with  felt  tape,  and  by  a 
layer  of  Manilla  yarns,  and  preservative  covering,  with  a  plaited 
exterior  of  yarns,  forms  an  excellent  land-line  cable  for  subterraneous 
work,  to  connect  firing  stations  either  for  tiring,  or  for  telegraphic  pur- 
poses. This  form  of  cable  can  be  made  up  very  conveniently  into  four 
or  seven-cored  multiples,  before  being  covered  with  the  yarns  and 
external  plaiting. 

Covered  Wires  for  the  Firing  Stations. — Protected  wires  of  a  less 
costly  nature  will,  however,  answer  every  purpose  for  the  connections 
in  the  firing  stations,  telegraph  stations,  and  test  rooms. 

The  Conductor. — The  conductivity  of  electric  cables  for  submarine 
mining  depends  to  a  great  extent  upon  the  sensitivity  of  the  electric  fuzes 
employed  in  the  mines,  and  in  succeeding  chapters  the  employment  of 
much  more  sensitive  fuzes  than  those  now  used  in  the  English  sub- 
marine mining  service  will  be  recommended,  it  being  possible  to  reduce 
the  current  required  to  fire  a  fuze  from  0.9  of  an  ampere  to  0.15 
ampere,  and  to  reduce  the  conductivity  of  the  cable  cores  in  like 
measure.  Thus  instead  of  the  conductor  offering  only  5  or  7  ohms 
resistance  per  1000  yards,  it  may  have  40  ohms  and  be  used  elliricntly 
in  connection  with  a  more  sensitive  fuze.  It  is,  howiNir,  advan- 
tageous to  possess  a  b'ne  of  low  conductivity  to  tlic  mine  wlun  liy  any 
cause  a  leak  lias  been  di'vclopcd  in  any  ]M)rtion  of  a  core,  ami  fur  this 
reason,  if  fur  no  other,   it  is  better  not  to  reduce  the  comlucti\  it  v  too 


Electric  Gnhhs.—Tke  Covductor. 


103 


much.  One-half  of  the  reductioii  above  mentioned  can  bo  taken  with 
perfect  safety,  however,  if  fuzes  of  higher  sensitivity  be  used.  The 
conductivity  resistance  per  1000  yards  may  perhaps  be  fixed  at  about 
18  or  20  ohms. 

The  conductor  slioukl  be  constructed  of  several  wires  twisted 
together,  because  greater  elasticity  in  a  longitudinal  direction,  as  well 
as  greater  pliability,  are  thereby  obtained.  It  is  sometimes  found  that 
the  conductor  is  broken  by  the  strains  thrown  upon  a  cable  during  sub- 
marine mining  operations,  and  the  question  arises  whether  a  conductor 
made  of  twisted  steel  wires  might  not  be  employed  advantageously 
instead  of  copper.  For  any  given  conductivity  the  steel  would,  how- 
ever, be  six  times  the  cross-section,  and  2|  times  the  circumference  as 
compared  with  copper,  and  the  amount  of  dielectric  covering  would 
be  increased  proportionally. 

No  experience  having  been  obtained  in  this  direction,  it  can  scarcely 
be  recommended  except  for  experiment,  but  it  appears  woi-thy  of  trial 
as  such,  for  the  steel  conductor  being  six  times  the  weight,  would  be 
twelve  times  the  strength  of  a  copper  conductor.  The  compound  wire 
(an  Amei'ican  invention)  now  manufactured  in  this  country  by  Messrs. 
Siemens  Brothers,  would  probably  form  an  effective  compromise. 

The  following  figui*es  are  taken  from  the  very  complete  Table  pub- 
lished by  Messrs.  Walter  Glover  and  Co.,  of  Manchester,  contractors  to 
Her  Majesty's  Postmaster-General,  &c.  : 

Table  XXXI. — Dimensions,  itc,  op  Pure  Copper  Wires. 


B.W.G. 

Diameter. 

Yards  per 
Pound. 

Yards  per 
Ohm. 

Re.marks. 

No. 

\n 

10 

.134 

6.133 

579.80 

stranded  conductors   weigh   more   and 

11 

.12 

7.647 

464.977 

offer  less  electrical  resistance  than  the 

12 

.109 

9.268 

383.637 

amounts  given  by  these  figures. 

1.3 

.095 

12.202 

291.417 

14 

.083 

15.985 

222.446 

The  electrical  resistance  increases  with 

15 

.072 

21.242 

167.302 

temperature   by  0.21    per  cent.    deg. 

16 

.065 

26.063 

136.425 

Fahr. 

17 

.058 

32.734 

108.624 

18 

.049 

45.863 

77.528 

The  Table  is  for  60  deg.  Fahr. 

19 

.042 

62.425 

56.960 

20 

.035 

89.892 

49.797 

The    weights     are    calculated    on    the 

21 

.032 

107.537 

33.065 

assumption  that  1  cubic  foot  of  pure 

22 

.028 

140.461 

25.315 

copper  weighs  555  lb. 

23 

.025 

176.190 

20.181 

24 

.022 

227.517 

15.628 

25 

.020 

275.294 

12.916 

26 

.018 

3.39.870 

10.462 

27 

.016 

4.30.147 

8.266 

28 

.014 

561.827 

6.329 

29 

.013 

651.587 

5.457 

30 

.012 

764.710 

4.650 

It  lieing  advantageous  to  use  a  number  of  small  wires,  No.  30  B.W.G, 


104  Submarine  Mining. 

may  be  selected,  and  it  will  be  found  that  twelve  such  wires  will  give 
the  conductivity  resistance  limit  already  mentioned,  viz.,  18  ohms  per 
1000  yards.  Thus  4.65x12  =  55.8  yards  per  ohm  for  such  a  strand, 
and  55.8  x  18,  or  1004  yards,  will  therefore  offer  18  ohms  resistance  at 
60  deg.  Fahr.  These  wires  should  be  aiinealed  and  tinned  before  they 
are  stranded. 

In  the  gutta-percha  covered  cores  for  multiple  cables,  the  conductor 
may  be  composed  of  a  strand  of  seven  No.  27  B.W.G.  copper  wires 
which  possess  the  same  conjoint  resistance,  18  ohms,  for  a  length  of 
1042  yards. 

The  Insulator. — Proceeding  outwards,  the  dielectric  employed  need 
not  be  so  thick,  nor  so  cai-efully  arranged  to  produce  high  resistance,  as 
in  submarine  cables  for  long  lines  of  telegraph,  a  comparatively  very 
low  insulation  resistance  being  sufficient  for  our  purposes.  But  it  is 
important  that  the  general  arrangement  of  the  covering  dielectric  shall 
be  such  as  to  insure  permanency  as  far  as  possible.  This  cannot  be 
shown  by  a  high  insulation  test  during  or  soon  after  manufacture,  but 
the  opinions  of  the  best  makers  should  be  sought,  and  their  advice 
followed  in  this  matter. 

The  gutta-percha  covered  cores  should  be  made  with  two  coatings  of 
gutta-percha  prepared  in  accordance  with  Mr.  Willoughby  Smith's 
patent ;  and  the  india-rubber  covered  cores  should  be  made  in 
accordance  with  Mr.  Hooper's  patent.  They  are  so  well  known  that 
they  need  not  be  described  here. 

The  main  cost  of  a  cable  is  due  to  its  core  or  cores.  I  repeat  that  a 
cheap  core  of  comparatively  low  insulation  resistance  will  act  efficiently 
for  submarine  mines  if  its  permanency  be  carefully  provided  for,  both 
chemically  and  mechanically,  by  a  tough  insulator  and  strong  pliable 
covering.  The  insulation  resistance  is  not  a  matter  to  haggle  about ; 
the  permanency  is.  The  weight  of  the  insulation  need  not  exceed  1  cwt. 
per  knot. 

Core  Covering. — Proceeding  outwards,  the  core  of  a  single  cable 
should  be  covered  with  a  serving  of  india-rubber  .coated  cotton  tape, 
wound  on  spirally  with  a  fair  overlap.  This  should  be  covered  by  a 
braiding  of  several  three-ply  line  hemp  twines,  and  the  whole  steeped  in 
a  protective  composition. 

The  Armouring.- — As  pliability  is  necessary,  combined  witli  strength 
and  durability,  strands  of  galvanised  steel  wire  should  be  employed.  A 
strand  composed  of  seven  No.  19  B.  W.G.  can  be  recommended,  with  say 
one  twist  in  about  2^  in.  Twelve  of  these  strands  will  cover  the  cable 
when  laid  on  with  one  turn  in  about  8J  in.  to  9  in. 

Tlie  Outer  Covering.^In   order   to    prevent  the  steel  strands  from 


Electric  CaJdrs.—Dcfaih.  105 

gaping  and  thereby  exposing  tlie  interior  core  to  the  attacks  of  marine 
life,  ikc,  an  outer  covering  of  braided  hemp  cords  should  be  added.  This 
braiding  should  not  bind  the  armouring  too  tightly,  or  the  conductor 
will  be  unduly  strained  and  perhaps  break  wlien  the  cable  is  bent  and 
in  tension. 

The  cable  should  now  be  steeped  in  a  preservative  compound. 

Dimensions,  d:c. — The  cable  will  then  be  about  fin.  in  diameter; 
it  will  weigh  about  a  ton  per  knot  (in  air)  ;  and  its  Ijreaking  strength 
will  slightly  exceed  5  tons.  Portions  of  it  sliould  be  tested  for  con- 
ductivity when  subjected  to  its  working  strain  of,  say,  1  ton,  and  a  clause 
should  figure  in  the  specification  to  that  effect.  Also  the  conductivity 
and  insulation  resistances  of  the  whole  length  should  be  found  during 
manufacture,  at  delivery,  and  periodically  afterwards,  records  of  same 
being  kept.  The  greatest  care  should  l)e  taken  to  see  that  the  steel 
wires  are  thoroughly  galvanised,  and  tiiat  the  galvanising  is  not  cracked 
during  the  process  of  stranding.  As  far  as  the  armouring  is  concerned, 
dry  storage  is  of  course  preferable  to  storage  under  water.  The  supply 
and  delivery  can  be  had  in  1-knot  lengths. 

Multiple  Cables. — Returning  to  the  multiple  cables,  the  four  or 
seven  cores  already  described  should  be  stranded,  and  then  wormed 
and  served  with  tarred  jute  yarn,  round  which  are  wound  about  four- 
teen No.  12  B.W.Gr.  galvanised  B.  B.  iron  wires  for  the  four-cored,  and 
about  sixteen  ditto  for  the  seven-cored  cable,  to  form  an  armouring.  A 
braiding  of  hemp  cords,  as  in  the  single  cable,  is  then  added,  and  the 
whole  steeped  in  a  preservative  composition.  The  four-cored  cable 
weighs  about  2  tons  in  air  and  1  ton  in  the  water — and  the  seven-cored 
cable  does  not  differ  greatly  from  it  in  these  respects. 

Shore  Ends.  —  When  cables  have  to  cross  rocks  or  shingle  exposed  to 
a  heavy  wash  from  the  sea,  it  is  desirable  to  employ  an  additional 
armouring  for  their  protection.  The  cable  so  employed  may  be  precisely 
similar  to  the  multiple-armoured  cables  just  described,  with  an  addi- 
tional serving  of  tarred  jute  yarn  and  a  sheathing  of  No.  1  B.W.G. 
(  =  0.3  in.  in  diameter)  B.B.  iron  galvanised  wii-es.  About  eleven  such 
wires  are  required  to  cover  the  four-cored,  and  twelve  to  cover  the  seven- 
cored  cables.  This  cable  being  stiff,  heavy,  and  difficult  to  coil  or 
manipulate,  should  be  laid  as  soon  as  possible  in  sitii.  The  manner  in 
which  cables  should  be  tested  periodically  will  be  described  hereafter  in 
the  paper  on  testing  stores. 

Crowning  Cables. — Cables  must  be  connected  to  the  mines  and  to 
each  other  both  electrically  and  mechanically.  For  this  purpose  the 
cable  end  should  be  made  into  a  crown,  a  padding  of  spun  yarn  being 
wound  round  the  armouring  about  1  ft.  from  the  end  of  the  cable,  and 


106 


Svhniarine  Minin(). 


the  wires  turned  back  and  whipped  witli  binding  wire  and  spun  yarn. 
The  miners  sliould  be  taught  to  make  these  crowns  in  accordance 
with  patterns  of  the  proper  sizes  and  dimensions  for  multiple  and  for 
single  cables.  They  will  then  fit  into  the  cable  grips  made  in  the  mine 
cases,  junction  boxes,  &,c.  The  projecting  foot  of  the  core  should  be 
protected  with  a  whipping. 

Electrical  Joints. — The  electrical  joints  used  in  sulnnariiie  mining  are 
very  similar  to  those  used  for  underground  telegraphs,  and  require  no 
special  notice.  Whenever  time  is  available  they  should  be  soldered  ; 
Fletcher's  soldering  apparatus  being  used  on  the  mine  fields.  Cable 
ends  when  crowned  can  be  connected  by  laying  them  together,  with 
about  6  in.  of  overlap,  and  lashing  with  binding  wire  and  spun  yarn. 
The  cores  can  then  be  connected  electrically,  and  the  whole  covered 
with  a  strong  bandage  of  canvas.  But  cable  ends  are  usually  con- 
nected by  what  are  termed  : — 

Fuj.  ^9. 


Box  for  connecting  2  Single  cables  Elec. 


Box  for  connecting  r 

Multiple  and  several 

Single  cables. 


Grip  tiLiok 


Contiectiug  Boxes. — These  can  be  made  of  cast  iron,  I'acli  in  two  lialf- 
pieces  connected  together  by  bolts  and  nuts,  as  shown  on  the  skctcli, 
Figs.  49  and  50.  The  bolts  should  lie  short;  the  heads  sninll,  and 
embedded  in  recesses  in  the  castings;  the  nuts  small,  but  deep,  and  also 
embedded  as  far  as  possible,  so  that  the  projections  may  not  foul  any- 
thing wlien  the  cable  is  paid  off  a  drum  or  coil  during  the  mining  opera- 
tions. The  boxes  for  connecting  multiple  cables,  four-coro  and  seven- 
core,  and   for  connecting   a  shore  end  with  an  ordinary  nniltiple  cable, 


Connecting  and  Jimction  Boxen.  107 

may  be  similar  to  the  above,  but  of  suitable  dimensions  to  grip  these 
larger  cables,  and  to  hold  the  seven-core  joints.  It  is  7iot  necessary  to 
illustrate  or  describe  them  further. 

It  is  sometimes  necessary  to  connect  three  cable  ends.  The  cast-iron 
box  can  then  be  made  as  shown  on  sketch  (not  the  English  pattern), 
see  Fig.  50.  It  should  be  large  enough  to  hold  a  small  apparatus 
called  a  disconnector,  to  be  explained  hereafter. 

Junction  Boxes. — As  explained,  multiple  cables  lead  to  a  number  of 
single  cables,  one  of  the  latter  to  each  core  of  the  former.  These  connec- 
tions are  made  in  what  is  termed  a  multiple  junction  box.  It  is  best  to 
have  only  one  pattern,  viz.,  for  one  multiple  and  seven  single  cables.  The 
same  box  will  then  do  very  well  for  the  multiple  four-core  cable  and 
four  single  cables.  It  is  often  necessary  to  buoy  the  junction  box  both 
during  and  after  the  mining  operations,  and  for  this  reason  it  should 
be  somewhat  heavy.  The  buoy  can  be  comparatively  small  and  be 
mooi'ed  to  a  light  line,  which  will  bring  up  a  chain  from  the  bottom 
wherewith  to  weigh  the  box  and  its  eight  cable  ends.  A  yV^^-  chain 
is  not  too  strong  for  the  work,  and  a  |-in.  chain  in  deep  water.  The 
multiple  cable  should  be  moored  to  a  heavy  sinker  at  a  distance  from 
the  box  of  about  twice  the  depth  of  the  water.  This  prevents  the 
system  being  dislodged  when  the  box  is  raised  for  any  purpose  by  a 
junction  box  boat  in  a  tideway.  If  the  human  hand  be  opened,  the 
thumb  kept  as  far  from  the  four  fingers  as  possible,  and  the  whole 
pressed  down  upon  the  table,  keeping  the  arm  vertical,  it  represents 
the  system,  the  arm  being  the  recovering  chain,  the  thumb  the  main 
cable  to  shore,  the  four  fingers  four  branch  cables  to  the  mines,  and  the 
palm  of  the  hand  the  junction  box.  It  is  better  to  make  the  box  heavy 
because  the  cables  are  then  less  liable  to  foul  one  another,  or  bottom 
obstructions.  It  makes  it  a  little  more  difficult  to  raise  the  system,  but 
a  foul  cable  is  far  worse.  The  box  should  probably  not  be  less  than 
2  cwt.  when  empty  and  on  shore.  Its  shape  should  be  circular  in  plan, 
as  this  gives  the  largest  interior  space  for  a  given  periphery,  and  also 
because  it  offers  no  corners  to  knock  holes  in  the  boats  when  raised  in 
a  seaway.  An  arrangement  of  the  kind  is  illustrated  in  Figs.  51,  52. 
The  plan  shows  the  box  with  the  wrought-iron  cover  removed.  The 
cables  are  secured  by  grip  hooks  (Fig.  48),  the  nuts  for  same  being 
readily  got  at.  The  sheet-iron  disc  covering  the  bottom  is  not  absolutely 
necessary,  but  it  protects  the  bottom  of  the  grip  hooks  from  blows,  and 
gives  a  neater  appearance.  The  thick  wrought-iron  lid  is  secured  to  the 
casting  by  three  strong  studs  and  nuts.  The  whole  is  recovered  by  the 
ring  in  the  centre  of  the  lid.  This  is  not  the  English  pattern,  but  is 
a  decidedly  better  and  stronger  arrangement.     When  the  branch  cables 


108  Suhrtiarine  Mining. 

lead  to  electro-contact  iiiinos,  the  main  cable  is  a  single  cable,  and  the 
junction  box  is  made  larger  in  order  to  hold  certain  apparatus  by  which 
each  mine  is  cut  oft'  from  the  system  when  fired,  and  by  which  tests  can 
be  taken  when  the  box  is  raised.  A  new  and  improved  apparatus  of 
this  kind  recently  designed  by  the  writer  will  be  descriljed  hereafter. 

Cable  Entry  to  a  Mine. — When  a  cable  is  taken  into  a  mine  it  is 
connected  to  one  leg  of  the  entrance  plug  electrically,  and  the  cable 
ci'own  is  gripped  by  a  cast-iron  dome  screwed  down  upon  it  at  the  same 
position  that  one  of  the  grip  hooks  occupies  on  the  sketch. 


109 


CHAPTER  IX. 

On  Electric  Fuzes. 

The  efficiency  of  a  submarine  mine  tired  and  controlled  by  electricity 
depends  to  a  great  extent  upon  the  constancy  and  reliability  of  the 
electric  fuze  that  is  employed.  Electric  fuzes  can  conveniently  be 
divided  into  two  classes,  viz.  : 

1.  High-resistance  fuzes. 

2.  Low-resistance  fuzes. 

The  former  can  be  ignited  by  small  currents  of  high  potential ;  the 
latter  by  larger  currents,  the  potential  required  being  much  lower 
because  the  electrical  resistances  in  the  fuzes  ai-e  insignificant. 

One  of  the  best  papers  ever  written  on  this  subject  came  from  tlie 
pen  of  Captain  (now  Major-General)  E.  W.  Ward,  Royal  Engineers, 
vide  Paper  XVI.,  vol.  iv.,  of  the  R.  E.  Professional  Papers,  published 
1855,  where  we  find  that  the  action  of  certain  high-resistance  fuzes 
then  in  use  depended  upon  "the  combustion  of  a  compound,  whicli 
seemingly  is  a  sulphuret  of  carbon  and  copper,"  and  that  these  fuzes 
were  "the  iiavention  of  Mr.  Brunton,  of  the  Gutta  Percha  Works  in 
the  City-road.  This  company  had  been  in  the  habit  of  what  is 
familiarly  called  vulcanising  the  gutta-percha  which  covered  the  wire, 
to  render  it  pliable  even  in  the  coldest  temperature,  and  this  led  to  the 
discovery  of  the  fuze  in  question.  By  the  vulcanising  process  sulphur, 
and,  I  believe,  carbon,  became  incorporated  with  the  gutta-percha. 
....  These  two  act  on  the  inclosed  copper  wire,  and  in  process  of 
time  produce  on  its  surface  a  species  of  sulphide,  portions  of  which, 
when  the  wire  is  withdrawn,  remain  adhering  to  the  inner  surface  of 
the  gutta-percha  covering.  This  inner  surface  ....  has  now  a  feeble 
power  of  conduction  given  to  it  by  means  of  the  minute  particles  of 
sulphide  of  copper  and  carbon.  The  conducting  power  is,  however, 
very  feeble,  and,  seemingly,  in  no  two  portions  the  same  ;  but  whatever 
the  amount  of  resistance  may  be,  if  it  can  be  overcome  sufficiently  to 
circulate  such  a  force  as  will  ignite  the  sulpiiur  and  carbon,  the  desired 
effect  is  obtained." 

In  Lieutenant-Colonel  (now   Major-General)  Stotherd's    "  Notes  on 


110  Suhmarine  Mining. 

Defence  by  Submarine  Minos,"  i)ul)li.slied  LSTo,  the  Beardslee  fuze  with 
grapliite  priming  and  the  Austrian  and  the  Prussian  fuzes  with  priming 
of  ground  glass  and  sulpiiur  are  described,  and  tlien  the  English 
service  submarine  mining  fuze  of  that  date  as  follows  :  "  Another 
similar  form  of  fuze  is  that  invented  by  Mr.  Abel,  F.R.S.,  chemist  to 
the  War  Department.  This  fuze  was  devised  and  experimented  with 
extensively  in  1858,  and  the  above  more  recently  designed  fuzes,  viz., 
Beardslee's,  the  Austrian,  and  the  Prussian,  are  based  upon  the 
principles  first  applied  to  that  fuze.*  It  has  been  modified  since  its 
first  invention  in  a  few  details.  .  .  .  Tlie  priming  of  the  original 
fuzes  consisted  of  10  parts  of  subphospliide  of  copper  prepared  by  a 
special  method,  45  parts  of  subsulphide  of  copper,  and  15  parts  of 
chlorate  of  potassa.  These  proportions  of  the  ingredients  are,  how- 
ever, now  varied  so  as  to  furnish  fuzes  of  different  degrees  of  conduc- 
tivity and  sensitiveness  to  suit  different  purposes." 

The  fuze  is  then  described  in  detail.  It  remained  the  service  fuze 
for  submarine  mining  for  several  years,  and  was  finally  abandoned  for 
several  reasons,  one  being  the  admitted  danger  that  mines  primed  by 
any  high-resistance  fuzes  might  be  accidentally  exploded  during 
magnetic  or  electric  storms,  either  by  induced  currents  or  by  the 
electric  discharge  of  the  cables  at  such  times.  It  appears,  also,  from 
a  sentence  in  General  Abbot's  book,  that  a  fear  of  the  effect  of  induced 
currents,  however  produced,  "  had  much  to  do  with  their  "  (similar 
fuzes)  "  ultimate  exclusion  from  "  the  American  submarine  mining 
service. 

Loiv- Resistance  Fuzes. — The  ignition  of  gunjjowder  by  a  thin  platinum 
wire  heated  by  the  passage  of  an  electric  current  had  already  "been 
long  in  use  "  when  Captain  E.  W.  Ward,  R.E.,  investigated  the  subject 
in  1855  ;  but  to  him  we  are  indebted  not  only  for  some  simple  and 
efficient  instruments  which  have  been  in  use  ever  since,  but  also  for 
treating  the  matter  scientifically,  in  precise  mathematical  tci-nis. 
Moreover,  tlie  form  of  wire  fuze  adopted  by  him  was  retained  in  our 
service  for  a  number  of  years,  and  tlie  men  taught  to  make  them. 

A  small  block  of  soft  wood  has  a  small  rectangular  cavity  cut  out 
of  one  side,  and  two  No.  16  percha-covered  wires  are  bared  at  tiie  ends 
and  passed  through  small  cross-holes  made  in  the  block.  The  platinum 
wire  is  then  soldered  across  them,  the  cavity  filled  with  meal  powder, 
and  a  thin  wooden  lid  screwed  down  upon  it.  See  Figs.  53  and  54. 
It  is  described,  both  on  account  of  tlie  history  of  the  low-resistance 
fuzes,  and  because  it  is  still  useful  as  a  method  of  improvising  fuzes  for 

*  This  is  not  correct.  The  principles  were  first  applied  in  the  Brunton  fuze, 
dcbcribed. 


Hvjh  and  Loiv  lieaistaiice  Fuzes 


111 


gunpowclei-  luiiK^s.  Tu  18G8  tlie  following  improvements  were  made 
by  the  author,  wlio  at  that  time  was  acting  as  assistant  instructor  of 
telegraphy  at  Cliatham. 


The  two  No.  16  wires  were  replaced  by  two  thick  wires  passed 
through  a  block  of  wood  shaped  like  an  ordinary  medicine  cork,  the 
platinum  wire  was  soldered  across  their  ends,  and  the  sensitivity 
greatly  increased  by  a  wisp  of  fibrous  gun-cotton  wound  round  the 
platinum  wire.  Also  the  fuze  was  converted  into  a  detonator  by  the 
employment  of  a  charge  of  mercurial  fulminate  contained  in  a  small 
tin  cylinder,  as  shown  in  Fig.  55. 


Fi^  55 


sa. 


The  employment  of  fulminating  mercury  to  convert  a  fuze  into  a 
detonator  had  already  been  adopted  in  connection  with  the  high- 
resistance  submarine  mining  fuze  already  desci'ibed,  but  up  to  the  time 
when  the  other  aljove  improvements  were  made  in  the  low-resistance 
fuzes,  it  was  generally  held  by  experts  in  England  that  these  fuzes  were 
inapplicable  to  submarine  mining  on  account  of  their  want  of  sensi- 
tivity, and  the  large  battery  power  necessary  to  fire  the  mines  at  any 
distance  from  the  battery.  Experiments  with  the  above  fuze  soon 
proved  that  this  view  was  erroneous,  and  although  the  inventor  was 
ordei-ed  abroad  in  the  middle  of  them,  they  were  continued,  and  the 
detonator  was  very  favourably  considered.  In  1871,  when  the  first 
edition  of  Captain  Stotherd's  "  Notes  on  Submarine  Mining  "  was  pub- 
lished by  the  Royal  Engineer  establishment,  the  fuze  was  described  by 
the  name  of  the  present  writer,  although  strictly  it  was  the  Ward 
fuze  improved.  The  next  important  improvement  was  made  by 
Captain  Fisher,  R.N.,  when  in  command  of  the  Vernon  Torpedo 
School.  He  carried  out  a  number  of  experiments  with  different  alloys 
in  the  bridge,  and  finally  selected  platinum-silver,  which  is  still  employed 
in  the  Royal  Navy  in  preference  to  other  alloys.  Captain  Fisher's 
investigations  may  be  said  to  have  nearly  perfected  the  fuze  as  now 
employed  in  the  Royal  Navy,  but  an  improved  wire  was  not  adopted 


112  Submarine  Mining. 

by  the  Royal  Engineers  until  three  years  later,  by  which  time  experi- 
ments had  been  made  with  different  wires  at  the  Chemical  Laboratory 
at  Woolwich,  as  recorded  on  an  important  memorandum  to  the  Society 
of  Telegraph  Engineers  by  Professor  Abel,  May  13,  1874.  The  out- 
come was  similar  to  Captain  Fisher's  experiments,  and  confirmed  those 
of  General  Abbot,  which  had  then  come  to  a  termination,  l)ut  had 
not  been  published,  viz.,  that  German  silver  is  liable  to  corrosion  ;  that 
platinum-silver  is  superior  in  this  respect,  but  difficult  to  draw  into  a 
fine  and  uniform  wire  ;  that  platinum-iridium  fulfils  the  required  con- 
ditions best,  being  easily  fused,  easily  drawn,  and  safe  against  corrosion, 
also  larger  in  diameter  than  platinum  wire  of  same  resistance,  and 
therefore  ofiering  more  surface  to  the  priming.  General  Abbot's  excel- 
lent report  on  fuzes  treats  the  subject  in  a  very  thorough  and  scientific 
manner.     He  recommends  that : 

1.  The  insulated  conducting  wires  for  all  fuzes  should  be  formed  of 
tough  and  flexible  copper  about  20  B.  W.  G.,  of  equal  length,  say  5  in. 
and  7  in.,  and  covered  with  a  closely  woven  wrapping  of  cotton  thread 
coated  with  paraffin,  or  with  beeswax,  resin,  and  tar  boiled  together. 
The  employment  of  gutta-percha  or  india-rubber  is  not  recommended, 
owing  to  deterioration  after  lengthened  storage. 

2.  The  plug  of  the  fuze  should  be  hard,  strong,  and  a  good  non- 
conductor of  electricity.  Beechwood,  kiln-dried,  and  coated  thickly 
with  Japan  wax,  is  recommended  in  preference  to  other  materials. 
The  following  form  has  been  adopted  into  the  American  service.  It  is 
in  three  parts.  First,  a  cylinder,  0.25  in.  in  diameter  and  0.7  in.  long, 
grooved  longitudinally  on  opposite  sides  to  receive  the  wires.  Entirely 
round  the  middle  is  a  cut  0.05  in.  deep  and  0.15  in.  wide.  The  wires 
are  carried  up  the  horizontal  grooves  for  half  the  length  of  the  cylinder, 
then  half  round  by  the  canelure,  and  up  the  remainder  of  the  cylinder 
on  opposite  sides.  The  inside  ends,  about  0.1  in.  long,  are  tlien  bared 
and  scraped.  Second,  a  hollow  cylindrical  cap  closely  fitting  above 
with  a  stout  shoulder  at  on(;  end,  against  which  the  solid  plug  aljuts 
when  it  is  forced  into  the  cap,  thus  leaving  a  smaller  hole  for  tlie  pas- 
sage of  the  free  ends  of  the  insulated  wires.  This  leaves  a  small 
chamber  round  the  bridge  for  the  priming,  about  4  grs.  of  mercurial 
fulminate,  and  the  chamber  is  closed  by  a  paper  disc. 

3.  The  detonating  cap  of  the  American  fuze  is  mivde  of  t'(i))ii(^r 
punched  into  cylindrical  form  to  fit  the  cap  closely.  It  contains  20  grs. 
of  mercurial  fulminate,  the  total  priming  therefore  being  24  grs. 

4.  The  American  fuze  is  1.4  in.  long  and  0.1  in.  in  tliametor.  It  is 
waterproofed  with  a  coating  of  Japan  wax. 

There  are  se\'eral  patterns  of  Ijiiglish  fuze  or  detonator,  tlic  Irrm  iu/.v 


English  Low-Resistance  Fuze. 


113 


being  applied  by  us  to  a  fuze  with  a  gunpowder  bursting  eliargo,  and 
tlie  term  detonator  to  a  fuze  with  a  bursting  charge  formed  of  some 
detonating  composition,  and  mercurial  fulminate  is  found  most  suitable 
for  this  purpose.  As  General  Abbot  experimented  with  more  than  one 
form  of  English  detonating  fuze,  and  his  report  has  been  published, 
they  cannot  be  considered  as  secret  or  confidential.  Moreover,  their 
important  points  have  been  made  the  subject  of  scientific  papers  read 
in  public  by  Sir  Frederick  Abel,  who  is  chiefly  responsible  for  the 
specifications  and  patterns  governing  their  manufacture  at  the  Royal 
Arsenal. 

Our  detonating  fuzes  are  now  made  with  an  ebonite  head,  in  which 
two  strong  copper  wires  or  rods  are  firmly  imbedded.  To  them  ai-e 
soldered  the  leads,  which  are  composed  of  multiple  copper  wires  gutta- 
percha covered.  An  inner  sheet-metal  cylinder  covers  the  pillar  ends 
and  bridge,  a  hole  being  left  in  the  cylinder  at  the  bottom  by  which  it 
is  filled  with  a  mixture  of  finely  powdered  gun-cotton  and  mealed  gun- 
powder in  equal  parts.  An  outer  cylinder  of  thin  metal  prolonged  into 
a  small  quill-shaped  chamber  contains  the  bursting  charge  of  25  grs. 
mercurial  fulminate.  The  entire  arrangement  is  shown  on  the  sketch. 
Fig.  56. 


85MeO 
The  bridge  is  |  in.    long,   and   may  Ije  formed   of   platinum   siher, 
33  per  cent,  platinum,  the  wire  used  being  0.0014  in.  in  diameter,  and 

I 


114  Submarine  Mining. 

weighing  2.1  grs.  per  10  yai-ds.  Its  resistance  (cold)  is  then  1.6  ohms, 
and  the  firing  current  about  0.27  ampfere.  When  a  platinum-iridium 
(about  10  per  cent,  iridium)  bridge  is  employed,  the  wire  being 
0.0014  in.  in  diameter,  or  weighing  3.4  grs.  per  10  yards,  it  has  an 
electrical  resistance  (cold)  of  1.05  ohms,  and  is  fired  by  a  current  of 
a1)out  0.17  ampere. 

"When  firing  a  number  of  charges  in  divided  or  "  forked  "  circuit,  it 
is  considered  by  experts  in  the  Royal  Navy  that  the  fuze  bridge  should 
be  composed  of  an  alloy  which  melts  at  a  low  temperature.  Platinum 
silver  has  a  lower  fusing  point  than  either  platinum  or  platinum- 
iridium.  It  has  therefore  been  chosen  for  use  in  the  naval  fuzes  and 
detonators  used  for  firing  broadsides  and  lines  of  countermines,  for 
which  purposes  divided  circuit  has  been  adopted,  no  doubt  for  some  good 
and  valid  reasons.  For  submarine  mining  purposes  the  charges  can 
always  be  fired  in  series,  and  the  best  fuze  then  seems  to  be  one  in 
which  the  bridge  is  composed  of  platinum-iridium.  The  submarine 
mining  fuze  employed  in  our  service  has  a  much  lower  resistance  than 
that  given  above,  the  wire  being  platinum-iridium  (10  per  cent,  iridium) 
0.003  in.  in  diameter,  and  weighing  1.55  grs.  per  yard.  The  firing 
current  is  about  0.9  ampere,  and  its  fusing  current  about  1.65  ampere. 
Its  resistance  (cold)  is  0.325  ohm,  and  0.74  ohm  at  fusing  point.  The 
employment  of  a  fuze  with  this  low  sensitivity  is  necessary  for  the 
particular  arrangements  employed  in  our  service  for  firing,  testing,  and 
controlling  the  mines,  but  as  these  arrangements  are  secret  and  confi- 
dential, and  as  moreover  they  are  not  recommended  by  the  present 
writer  for  general  adoption  for  war  purposes  on  account  of  their 
intricacy,  and  the  difiiculties  consequently  encountered  in  training  men 
to  satisfactorily  perform  the  various  operations,  to  say  nothing  of  the 
utter  impossibility  to  fill  their  places  pi'omptly  in  the  event  of 
numerous  casualties  occurring,  the  adoption  of  a  more  sensitive  fuze  or 
detonator,  and  of  a  much  simpler  general  arrangement  in  the  test  and 
firing  stations,  is  and  will  be  recommended  on  these  pages.  As  regards 
the  temperature  of  the  wire  necessary  for  ignition,  and  the  best  priming 
to  employ  around  the  wire  bridge.  General  Abbot  makes  some  very 
pertinent  remarks.  He  notes  that  gun-cotton  flashes  at  428  deg. 
Fahr.  and  mercurial  fulminate  at  392  deg.  Fahr.,  but  that  the  latter 
being  a  better  conductor  of  heat  lowers  tlie  temperature  of  the  bridge 
more  rapidly,  and  requires  a  slightly  stronger  current  to  fire  tlie  fuze. 
Nevertlieless  lie  prefers  the  fulminate  priming  on  account  of  its  greater 
uniformity  in  results,  due  probably,  he  says,  to  its  greater  weight 
bringing  it  more  thoroughly  in  contact  with  the  bridge.  He  adds, 
"  Wliile  not  a  singh;  instance  of   failure;   has  been  recorded  among  tlie 


Theory  of  Loiv- Resistance  Fuzes.  115 

thousands  of  fulminate  of  mercury  "  primed  "  fuzes  used  in  these  in- 
vestigations, several  gun-cotton "  primed  "  fuzes  have  failed  by  the 
deflagration  of  the  wire  without  the  ignition  of  the  gun-cotton  priming." 
It  may,  however,  be  accepted  that  the  gun-cotton  priming  is  very  effi- 
cient and  quite  reliable  when  care  is  taken  to  insure  good  packing. 
Some  authorities  recommend  the  wisp  of  gun-cotton  (already  referred 
to)  improved  by  soaking  it  in  collodion  ;  but  it  is  difticult  to  remove 
all  traces  of  acid  from  long  staple  gun-cotton,  and  the  other  devices 
descri))ed  are  consequently  preferable.  The  heat  theoretically  produced 
in  the  wire  bridge  of  a  fuze  may  be  considered  as  follows  : 

If  H  be  the  number  of  units  of  heat  developed  by 
C  an  electric  current  in  amperes  through 
R  a  resistance  in  ohms  in 
T  seconds  of  time, 
H  =  C^RT. 
If  p  be  the  specific  resistance  of  alloy  used, 
/  be  the  length  of  bridge,  and 
r  its  radius, 
K—pl~T  »■-.. 
.-.  -K=C'-Tpl^Tr-. 
But  the  rise  of  temperature  x  of  the  fuze  wire  varies  directly  as  H 
and  inversely  as  S  the  specific  heat  of  the  alloy,  and  the  mass  of  the 
wire  I  X  ttt". 
Consequently, 

=  C^Tpl-.-Sl(irr-)". 
=  C^Tp^STr"r*. 

The  whole  mathematical  theory  of  the  bridge  of  a  wire  fuze  is 
examined  with  great  care  by  General  Abbot  in  his  report,  page  227  et 
seq.  ;  but  the  above  short  method  is  sufficient  to  indicate  the  chief 
points  of  theoretic  importance,  viz.  : 

1.  That  the  alloy  should  possess  the  highest  possible  specific  resist- 
ance ; 

2.  Combined  with  a  very  low  specific  heat ; 

3.  That  the  cross-section  of  the  wire  should  be  as  small  as  possible 
consistent  with  strength. 

But  another  point  does  not  enter  into  the  formula,  viz.,  loss  of  lifat 
by  conduction  through  the  priming,  and  by  conduction  through  the 
metallic  pillars  of  the  fuze.  The  former  has  already  been  alluded  to. 
The  latter  can  be  met  by  making  the  bridge  of  sufficient  length,  a  wire 
of  large  section  requiring  a  longer  bridge,  which,  however,  should  never 
be  longer  than  is  necessary  for  producing  the  required  sensitivity. 

In  the  American  service  the  maximum  current  required  for  working 


116  Submarine  Mining. 

their  automatic  arrangements  on  shore  for  firing  the  mines  is  0.15 
ampere,  and  as  the  bridge  heat  varies  as  the  square  of  the  current, 
allowing  10  as  a  margin  of  safety,  the  firing  current  has  been  fixed  by 
them  at  ^10  (0.15)- =  0.47  ampere.  For  fixing  the  bridge  wires  they 
use  a  solder  which  melts  (with  resin  flux)  only  at  a  high  tempei'ature. 
The  pillars  are  notched,  put  on  the  plug,  tinned  and  gauged  to  the 
exact  length  of  bridge.  The  wire  is  then  soldered  on,  and  the  pillars 
bent  slightly  inwards,  so  as  to  take  off  any  tension  on  the  bridge. 

When  automatic  arrangements  ai-e  not  employed  at  the  firing  and 
testing  stations,  more  sensitive  fuzes  than  those  adopted  for  the 
American  submarine  service  can  be  employed. 

Diiiconnecting  Ftizes. — Various  electrical  devices  have  been  proposed 
and  adopted  by  different  nations  for  automatically  cutting  off  a  branch 
cable  when  a  mine  at  the  end  of  it  is  exploded.  When  low-resistance 
detonators  are  used  in  the  mine  an  excellent  arrangement  is  to  use 
a  similar  low-resistance  fuze  as  the  cut-off".  No  detonating  charge  is 
employed,  but  a  minute  charge  of  pressed  meal  gunpowder  is  placed  in 
a  small  tube  having  its  end  just  below  and  pointing  on  the  bridge.  The 
rush  of  gas  caused  by  the  ignition  of  this  small  charge  breaks  the 
bridge  wire,  if  the  current  has  not  already  done  so. 

The  simultaneous  ignition  of  two  or  more  fuzes  on  continuous  circuit 
can  be  assured  when  the  fuzes  are  well  designed  and  made  chemically 
and  mechanically  similar  to  one  another,  and  the  current  is  sufficient. 
Their  minimum  firing  current  is  then  very  uniform.  But  a  firing 
current  should  be  used  in  practice  that  is  at  least  equal  to  their  fusing 
current,  in  order  that  all  the  fuzes  may  be  ignited  simultaneously  with 
certainty.  The  explosion  or  detonation  of  the  charges  surrounding 
them  does  not  then  affect  the  problem,  because  "  the  time  needed  to 
raise  the  temperature  of  the  bridge  to  the  requisite  degree  "  is  thereby 
"made  less  than  the  minimum  required  to  perform  the  mechanical 
work  of  explosion"  (Abbot).  When  a  weaker  current  is  used,  tlie  time 
required  to  heat  a  slightly  insensitive  fuze  may  be  less  tiiau  tlic  time 
occupied  by  the  explosion  of  a  neighbouring  charge,  and  a  blind  charge 
be  thereby  produced.  These  remarks  apply  equally  to  the  more  com- 
plex problems  connected  with  rock  blasting,  in  which  large  numbers  of 
fuzes  are  ignited  simultaneously. 

In  submarine  mining  we  have  two  fuzes  in  a  mine  and  one  in  tlie 
disconnector,  three  in  all.  Also  several  mines  are  sometimes  fired 
simultaneously,  perhaps  as  many  as  five  mines,  when  there  would  be 
ten  fuze  detonators  in  continuous  circuit. 

Extremdy  Sensitive  Wire-  Fuzes. — For  some  purposes  connected  \\\{\\ 
submarine  mining  extremely  sen.sitive  wire  fuzes  may  lie  employed  witli 


Disconnect hi(j  Fuzes,  d-c.  1 17 

advantage.  Such  fuzes  and  detonators  aro  onii)loyed  in  the  Danish 
service  for  certain  purposes,  but  their  manufacture  is  a  secret.  General 
Abbot  has,  however,  investigated  the  matter  with  his  customary  care 
and  accuracy.  He  employs  very  fine  wires  composed  of  an  alloy  of 
platinum  and  some  other  metal,  such  as  silver,  that  can  bo  removed  by 
oxidation,  ikc. 

Short  lengths,  O.l  1  in.  long,  of  the  wire  are  soldered  to  copper  wire 
terminals,  and  are  bent  outwards  into  loops.  They  are  then  covered  with 
wa.K,  except  about  0.08  in.  at  the  centre,  which  is  subjected  to  the  action 
of  nitric  acid,  and  the  silver  removed  chemically.  The  final  result  is  a 
short  length  of  platinum  wire  as  small  as  0.0002  in.  in  diameter,  which 
when  used  in  a  carefully  primed  fuze  with  the  above  bridge  length  can 
be  fired  by  a  current  of  about  0.04  ampere.  Adopting  Abbot's  co- 
efficient of  safety,  viz.,  ^/lO  c',  where  c  is  the  safe  current  that  can  be 
passed  through  a  fuze  which  can  be  fired  by  a  current  =  ;^10  c\  and 
equating  this  with  the  minimum  current  which  will  fire  the  platinum- 
iridium  fuze  described  at  top  of  page  1 1 4 ;  we  have  0. 1 7  =  ^1 0  cl  Hence, 
c  =  0.17-r  ^10^=0.054  ampere.  But  0.04  ampfere  is  suflicient  to  fire 
the  very  sensitive  fuze.  Consequently  the  latter  can  be  fired  by  a 
current  which  is  quite  safe  to  send  through  the  former. 

The  following  curiosity  among  fuze  designs  is  termed  the  "  Browne 
compound  fuze,  high  and  low  tension,"  and  consists  of  a  platinum  wire 
fuze  at  one  end  and  a  high  tension  fuze  at  the  other,  with  the  poles 
connected  by  two  5-ft.  lengths  of  No.  22  copper  (insulated)  wire 
wound  round  the  fuze.  The  firing  leads  are  connected  to  the  pillars  of 
the  high  tension  portion  of  the  arrangement.  A  current  of  0.85 
ampere  through  the  main  leads  fires  the  Avire  fuze,  and  a  current  of 
frictional  electricity  fires  the  high  tension  composition  ;  thus  proving 
what  nonsense  is  accepted  concerning  the  absolute  protection  afforded 
by  lightning  conductors.  Mr.  Browne's  composition  consists  of  mer- 
curial fulminate  four  parts,  sulphuret  of  antimony  one  part,  and 
powdered  antimony  three  parts. 

In  conclusion,  fuzes  for  submarine  mining,  whatever  may  be  the 
pattern  selected,  should  be  so  designed  as  to  be  mechanically  strong, 
chemically  permanent,  electrically  uniform.  Moreover  they  should  be 
manufactured  with  the  greatest  care,  stored  in  a  suitable  manner,  so  as 
to  protect  them  from  damp,  and  tested  periodically  to  prove  that  they 
remain  in  an  efficient  condition. 

The  wire  employed  in  the  manufacture  of  fuzes  is  generally  supplied 
from  a  well-known  contractor,  and  the  specification  governing  such 
supply  should  state  the  weight  of  a  given  length  taken  hap-hazard  in 
grains;  its  resistance  at  GO  deg.  Falir.  in  ohms;  the  fusing  current  in 


118  Sithmarine  Mining. 

amperes  when  passed  through,  say  |-  ia.  length  ;  tlie  lii-ing  current  in 
amperes  when  passed  through  same,  primed  in  the  required  manner  ; 
and  tlie  chemical  composition  of  the  wire. 

The  periodical  tests  of  the  fuzes  should  consist  of  resistance  tests 
and  sensitivity  tests.  Limits  should  be  laid  down  to  govern  these 
tests.  The  boxes  should  be  marked,  and  records  kept  of  the  tests  and 
dates. 


119 


CHAPTER  X. 

Electrical  Arrangements  on  the  Mine  Fields:  In  the 
Mines,  Circuit-Closers,  ike. 
Obsermtion  Mines.— T:ho  electrical  arrangements  in  connection  with 
observation  mines  may  be  of  the  simplest  possible  form,  viz.,  insulated 
conductor  from  firing  station,  through  fuzes  in  mine  (or  mines,  two  or 
more  being  sometimes  fired  simultaneously),  to  "  earth,"  in  the  sea,  and 
thence  by  "  earth  return." 

The  electrical  resistance  is  then  the  only  test  which  can  readily  be 
taken  to  judge  of  the  efficiency  or  otherwise  of  the  system,  and  it  is 
probably  sufficient ;  but  opinions  differ  on  this  point,  many  experts 
considering  that  an  apparatus  should  be  placed  in  the  mine  (or  the  end 
mine,  if  more  than  one),  which  will  indicate  the  efficiency  of  the  system 
more  thoroughly. 

A  small  electro-magnet  is  probably  the  best  apparatus  to  employ,  the 
movement  of  its  armature  by  a  small  electric  current,  that  can  be  sent 
through  the  fuzes  safely,  giving  indications  at  the  firing  station  that  the 
system  is  in  working  order.  These  indications  can  be  seen  by  means  of 
a  galvanometer,  or  heard  through  a  telephone.  The  apparatus  should 
be  so  arranged  that  it  will  cease  to  act  properly  when  wet,  and  it  should 
be  placed  at  the  bottom  of  the  small  chamber  containing  the  priming 
charge  of  the  mine.  Should  this  chamber  leak,  it  is  tlien  at  once  dis- 
covered. 

Any  electrical  engineer  can  design  such  an  instrument  in  half  an  hour, 
so  no  more  need  be  said. 

Mines  with  Circuit-Closers.— But  an  instrument  may  be  designed 
which  is  not  only  capable  of  testing  the  mine  or  circuit-closer,  but  also 
of  controlling  the  electrical  connections  therein.  The  author  believes 
that  he  was  the  first  to  propose  such  an  arrangement,  on  the  9th  March, 
1871.  The  following  were  the  words  used  in  the  memorandum:  "A 
quantity  battery  is  in  connection  with  the  upper  plate  of  a  switch  or 
commutator.  A  tension  battery  connects  with  the  lower  plate  ;  and 
the  third  plate  on  which  the  axis  of  the  switch  handle  is  fixed  connects 
with  the  cable.     Tlie  mine  may  be  incorporated  with  the  circuit-breaker 


120  Submarine  Mining. 

or  be  below  it,  and  separate,  but  in  either  case  the  tension  fuze  is  kept 
insulated  from  the  cable.  One  pole  of  the  fuze  is  put  to  earth,  and 
the  other  is  in  connection  with  the  metallic  uprights  of  Mathieson's 
inertia  circuit-closer,  modified  so  as  to  be  also  a  circuit-breaker.  Inside 
this  is  an  arrangement  consisting  of  a  coil  of  rather  thick  wire  wound 
round  two  soft  iron  cores  with  an  armature  pivotted  centrally  between 
them.  On  the  axis  of  this  armature,  and  fixed  to  it,  is  an  ebonite  disc, 
across  which  a  metallic  wire  is  led.  A  fixed  metallic  point  in  connec- 
tion with  the  shore  cable  presses  against  a  small  angular  return  on  the 
circumference,  and  near  the  bottom  of  the  disc.  At  or  near  the  other 
end  of  the  disc  wire  are  two  metallic  points,  one  in  connection  with 
the  standard  of  the  inertia  bob,  and  the  other  with  the  fuze,  or  with 
the  metallic  uprights  already  referred  to,  these  being  insulated  but  in 
connection  Avith  one  pole  of  the  fuze.  The  armature  is  kept  open 
by  a  small  spring,  or  by  a  preponderance  in  the  disc.  The  action 
is  as  follows  :  If  required  to  fire  by  contact,  the  tension  battery  is 
switched  to  cable  and  a  constant  current  passes  along  line  to 
the  cii'cuit-breaker.  This  current,  however,  is  not  of  sufficient  quantity 
to  form  an  electro-magnet  and  attract  the  armature.  As  soon  as  a 
ship  strikes  the  circuit-breaker  the  bob  leaves  dead  '  earth,'  and  strikes 
against  the  uprights,  and  the  tension  current  is  thus  switched  through 
fuze  and  fires  it.  Again,  if  it  be  required  to  fire  the  miiie  by  judgment, 
two  motions  of  the  switch  handle  in  quick  succession  are  necessary." 

The  quantity  battery  thus  attracts  the  armature,  and  the  tension 
battery  fires  the  mine  before  the  armature  returns  to  its  normal  posi- 
tion. This  arrangement  gave  power  to  test  line  for  insulation,  and  also 
for  movement  of  armature  ;  but  this  was  not  noted  on  the  memorandum. 

There  were  several  defects  in  this  arrangement,  and  it  is  only  de- 
scribed as  a  matter  of  historical  interest. 

On  the  following  year  Captain  (now  Lieutenant-Colonel)  R.  Y. 
Armstrong,  R.E.,  invented  a  much  better  arrangement,  which  was 
eventually  adopted  into  the  English  service. 

Its  present  more  elaborate  and  perfected  form  is  a  secret,  luit  the 
broad  principles  are  described  in  Stotherd's  "Notes  on  Submarine 
Mining,"  published  in  1873. 

It  consists  of  a  polarised  electro-magnet,  its  armature  being  pivotted 
centrally  between  the  four  poles  of  the  electro-magnet,  wliich  latter  is 
wound  by  a  coil  of  thick  wire  ottering  small  resistance,  and  by  a 
separate  coil  of  fine  wire  ofi'ering  a  high  resistance. 

One  end  of  the  thick  coil  and  one  end  of  the  fine  coil  are  generally 
connected  to  "  line,"  whether  the  apparatus  be  placed  in  a  mine  or  in  a 
detached  circuit-closer.      The  otliei-  end  of  tlie  thick   coil  is  generally 


A rmstrong's  Relaij. 


121 


connected  to  a  stop  against  whicli  tlie  armature  impinges  and  rests 
when  attracted  to  the  electro-magnet.  The  other  end  of  the  fine  coil  is 
generally  connected  to  earth.  The  armature  is  generally  connected  to 
earth,  and  in  the  mine  this  path  generally  traverses  the  fuzes.  A  small 
positive  or  negative  current  from  the  testing  station  gives  a  small 
deflection  on  a  low  resistance  galvanometer,  and  an  increased  positive 
current  gives  a  large  deflection  due  to  the  armature  in  the  mine  being 
attracted  to  the  stop  ;  also  an  increased  negative  current  produces  a 
similar  effect,  due  to  the  movement  of  the  armature  in  the  circuit-closer. 

Thus  the  presence  both  of  mine  and  of  circuit-closer,  in  a  presumably 
eflicient  condition,  are  indicated. 

The  mine  can,  of  course,  be  fired  by  the  application  of  a  positive 
current  of  sufficient  strength  at  any  time,  and  when  it  is  desired  to  fire 
it  automatically  on  a  vessel  striking  the  circuit-closer,  a  constant 
electric  potential  is  kept  on  the  system  insufficient  to  actuate  the 
armatures  in  either  mine  or  circuit-closer,  but  sufficient  when  the 
resistance  of  the  circuit  to  "  earth  "  in  the  circuit-closer  is  greatly 
reduced  to  produce  a  current  that  not  only  attracts  the  mine  armature, 
but  also  actuates  certain  apparatus  on  shore  which  automatically 
switches  in  the  firing  current  and  explodes  the  mine.  The  sketch  on 
Fig.  57  shows  this  arrangement  as  described,  but  the  instrument  is 
provided  with  several  terminals,  and  semi-permanent  connections  which 
can  be  easily  altered,  so  that  a  large  number  of  permutations  and  com- 
binations are  possible  with  two  or  more  of  these  instruments,  connected 
up  so  as  to  work  differently  with  positive  and  negative  currents. 
Armstrong's  Apparatus.  ^^ 


Fig.  58. 


The  ingenuity  of  the  novice  at  submarine  mining  is,  therefore, 
frequently  directed  towards  the  discovery  of  some  new  method  of 
connecting  up  these  instruments. 

They  have  not  been  adopted  by  the  Royal  Navy,  wliich  service  aims 
at  the  greatest  simplicity  in  all  arrangements  connected  with  sea 
mining.  For  the  same  reason  automatic  signalling  arrangements  at  the 
firing  station  are  also  omitted.     The  difficulty  lies  in    obtaining  high 


122  Submarine  Mining. 

efficiency  with  great  simplicity.  This  will  be  aimed  at  in  the  gear 
descriljed  on  tliese  pages.  We  shall  thereby  also  steer  clear  of  the 
apparatus  adopted  into  our  own  service,  which  certainly  is  not  re- 
markable for  simplicity,  however  great  may  be  its  efficacy  as  claimed 
by  those  who  have  elaborated  it. 

Circuit-Closers. — A  circuit-closer  is  a  device  for  bridging  a  gap  in 
an  electric  circuit  when  a  vessel  strikes  the  buoyant  body  containing 
the  apparatus.  The  earlier  forms  were  intricate,  costly,  and  inefficient. 
For  instance,  the  Austrian  pattern  exhibited  at  the  Paris  Exhibition  of 
1867  had  nine  projecting  arms,  each  with  a  spiral  spring,  each  with  a 
water-tight  joint,  and  all  or  any  of  them  actuating  a  central  ratchet 
wheel  on  a  vessel  striking  the  case.  A  partial  revolution  of  the  wheel 
produced  the  desired  electric  contact,  and  if  the  mine  was  not  tired,  the 
wheel  and  plunger  or  plungers  returned  to  their  normal  positions. 

A  circuit-closer  designed  by  Professor  Abel,  about  same  date,  was  a 
great  improvement.  The  radial  arms  were  replaced  by  a  disc  on  the 
top  of  the  case,  and  slightly  larger  in  diameter.  Tlie  disc  was  connected 
to  the  apparatus  by  a  flexible  and  water-tight  collar.  When  a  vessel 
struck  the  edge  of  tlie  disc  it  efiected  an  electric  contact  in  the  appa- 
ratus, in  a  manner  that  can  be  readily  imagined.  The  Abel  circuit- 
closer  is  a  reliable  apparatus  and  possesses  the  advantage  of  insensitivity 
to  signalling  by  the  explosion  of  countermines  in  its  vicinity.  The 
pressures  produced  by  such  explosions  miglit  damage  the  flexible  j oint, 
but  this  could  be  guarded  against  without  much  difficulty.  It  is  quite 
possible  that  some  modification  of  the  Abel  circuit-closer  may  again  be 
applied  to  submarine  mining. 

The  circuit-closer  which  has  found  most  favour,  however,  depends  in 
its  action  upon  the  inertia  of  a  small  movable  body  placetl  inside  the 
buoyant  case.  Such  an  apparatus,  designed  by  Quarter-Master  Sergeant 
Mathieson,  R.E.,  was  introduced  at  Chatham  soon  after  the  one  just 
mentioned.  It  consisted  of  a  lead  ball  on  a  steel  spindle,  the  inertia  of 
the  ball  causing  the  spindle  to  bend  when  the  case  was  struck  by  a 
vessel,  the  flexure  of  the  spindle  producing  the  desired  electric  con- 
tact by  means  of  a  ring  carried  against  suitable  springs  fixed  radially 
around  it.  This  circuit-closer  was  adopted  into  our  service  and  used 
for  many  years. 

In  July,  1873,  Mr.  Mathieson  patented  certain  improvements.  After 
describing  the  above  apparatus  in  his  specification,  he  notes  an  impor- 
tant defect  as  follows  :  "  Tliis  vibrating  rod  has  hitherto  consisted  of  a 
straight  rod  of  steel,  which,  if  not  tempered  to  exactly  the  proper 
degree,  will,  when  set  violently  vibrating  by  a  passing  vessel,  either 
snap  in   two  l)y  Ix'ing  too  liard  a  temper,   or  bend  a  little  and  take  a 


CircitU-Closers.  123 

perinannnt  set  if  of  too  soft  a  temper,  and  thcroliy  tlirow  the  adjust- 
ment out  of  order  and  render  the  apparatus  useless."  "To  remedy 
these  inconveniences  I  use  instead  of  the  straight  steel  I'od  a  long 
length  of  stout  wire  coiled  in  the  form  of  a  helix,  on  which  is  fixed  a 
short  spindle  with  the  weight  on  top.  .  .  ."  These  apparatus  in  their 
turn  were  adopted  into  our  service  and  a  large  number  purchased. 
They  are  still  serviceable  and  eflficient. 

The  next  improvement  was  designed  by  the  author  in  December, 
1876,  and  is  shown  on  Fig.  58.  a  is  a  coiled  spring  of  sufficient  power 
to  hold  the  small  ball  b  in  one  position  unless  the  apparatus  receive  a 
shock  ;  c  is  a  silk  cord  connected  with  an  adjusting  screw  s  at  one  end, 
and  with  the  spring  detent  d  at  the  other.  If  a  vessel  strike  the  buoy 
containing  this  apparatus,  the  ball  b  is  thrown  sideways  against  the 
cord,  and  this  pulls  d  and  releases  the  wheel  iv,  which  is  actuated  by 
clockwork  and  makes  a  complete  revolution  slowly,  during  which  period 
of  time  the  cable  is  connected  through  the  fuzes  to  "earth,"  and  the 
mine  can  be  fired  if  desired.  This  mechanical  retardation  gives  time  to 
the  operators  at  the  firing  station  to  discover  whether  the  circuit-closer 
has  been  operated  by  the  shock  of  a  countermine  or  by  the  blow  from 
the  vessel  of  a  foe.  From  300  to  400  contacts  were  obtained,  when  the 
clockwork  ran  down.  This  was  its  defect,  for  no  record  could  easily  be 
obtained  showing  the  number  of  contacts  expended.  The  apparatus 
was  improved  by  Major  (now  Lieut. -Col.)  R.  Y.  Armstrong,  R.E.,  who 
substituted  a  small  polarised  electro-magnet  for  the  clockwork,  and 
arranged  for  the  armature,  normally  out  of  the  magnetic  field,  to  be 
drawn  up  into  same  by  the  cord  c  when  the  circuit-closer  is  struck. 
There  it  remains  until  the  mine  is  fired  or  until  a  suitable  releasing 
current  is  sent  through  the  electro-magnet,  caushig  the  armature  to 
spring  back  into  its  normal  position. 

The  scientific  instrument  makers  of  the  School  of  Military  Engineer- 
ing have  worked  unremittingly  for  several  years  upon  this  germ,  and 
have  produced  a  complex  instrument  more  suitable  for  the  lecture  table 
than  for  active  service. 

In  December,  1881,  the  author  drew  up  the  following  description  of 
a  sinijde  apparatus  which  he  believed,  and  still  believes,  is  sufficient  for 
all  practical  purposes.  It  was  never  forwarded  officially,  other  work 
interfering,  and  was  put  aside  until  now.  In  Fig.  -59,  M  M  is  a  perma- 
nent horseshoe  magnet,  containing  the  ball-and  string  apparatus  already 
described.  To  tlie  poles  N.  S.  of  the  magnet  are  secured  the  cores  of 
two  small  low-resistance  electro-magnets  C  C,  one  end  of  the  coil  wire 
being  connected  to  "  line,"  and  the  other  to  a  contact  stud  b.  The 
armature  A  is  secured  by  a  spring  to  the   fixed   insulated   point   P, 


124 


Submarine  Mining. 


whence  an  insulated  wire  is  caiiied  through  the  fuzes  to  "  earth. '  The 
other  end  of  the  armature  spring  carries  a  contact  stud  n  wliich  engages 
witli  b,  wlieu  tlic  armature  is  attracted  to  n  s  the  poles  of  the  electro- 
magnet, which  are  fitted  with  small  ivory  distance  pegs,  preventing 
absolute  contact  between  the  armature  and  the  cores  of  the  electro- 


magnets, and  thus  avoiding  magnetic  adhesion.  A  set  spring  Q  adjusts 
the  strength  of  the  armature  spring.  The  magnets  are  shaped  like 
those  in  an  Ader's  telephone.  The  top  portion  is  perforated  and  tapped 
to  carry  the  screw,  and  for  regulating  the  tension  of  the  pull  cord,  and 
a  small  nut  K  clamps  same.  An  india-rubber  ring  r  tied  to  a  metal  ring 
prevents  the  ball  B  from  oscillating  too  violently.  The  various  portions 
of  the  apparatus  are  clamped  to,  or  carried  by,  strong  brass  standards, 
which  are  secured  to  a  metal  base. 

When  employed  as  a  detached  cii'cuit-closer  for  a  laige  mine  below  it, 
the  stud  b  is  connected  to  "  earth  "  through  an  interposed  I'csistance  of 
about  1000  ohms,  and  in  all  cases  P  is  connected  to  "earth"  through 
the  fuzes. 

I'iring  by  Observation. — The  apparatus  acts  as  follows.  The  coils  C  C 
are  wound  so  that  a  negative  current  from  shore  increases  the  normal 
polarity  of  the  soft  iron  cores,  conseciucntly  when  the  negative  pole  of  a 
firing  battery  is  connected  with  "  line,"  a  current  passes  through  the 
coils  C  C  and  the  1000  ohms  resistance  to  "  earth,"  causing  tlic  arma- 
tun;  A  to  be  attracted  to  the  electro-magnet,  and  tlioreby  sluinting  a 
current  through  the  fuzes  to  "earth,"  the  resistance  on  the  fuze  cirt'iiit 
being  low  enough  to  cause  the  mine  to  be  exploded. 

Firing  bj/  CoiUact.- — On   tlic  other  hand,  if  it  lie  di^sired  to  fu"e  l)y 


Glrcuit-Closers. 


125 


contact  the  negative  pole  of  a  weak  but  constant  l)attory  (a  few  Daniiill's 
cells)  is  connected  to  "line,"  and  when  the  circuit-closer  is  struck,  the 
armature  is  pulled  up  mechanically  and  retained  in  that  position  mag- 
netically. The  signalling  battery  gives  a  signal  on  shore  and  the  firing 
current  can  now  be  switched  to  line  or  not  as  desired,  the  mine  struck 
being  indicated  at  the  firing  station  by  a  deflection  on  a  galvanometer, 
and  by  causing  an  electric  bell  to  be  rung  in  a  manner  to  be  described 
hereafter,  when  the  arrangements  on  shore  are  examined.  Only  one 
mine  with  a  detached  circuit-closer  arranged  in  this  manner  can  be  put 
on  one  core. 

Electro-Contact  Mines. — When,  however,  the  apparatus  is  emiiloyed 
in  electro-contact  mines,  pure  and  simple,  the  "  earth "  wire  from  b 
through  a  1000  ohms  coil  is  omitted.  Several  mines,  say  six  or  seven, 
can  then  be  connected  with  one  core  or  single  cable,  either  in  a  string, 
one  after  the  other,  or  on  fork  (see  Figs.  60  and  61). 


In  the  former  case  connecting  boxes,  as  shown  in  Fig.  50  (see  page 
106),  are  used  ;  in  the  latter  a  junction  box,  about  to  be  described. 

When  any  mine  on  a  group  is  struck,  the  weak  current  battery  in 
the  firing  station  holds  up  the  armature  and  deflects  the  galvanometer 
connected  with  the  core  leading  to  that  group.  The  tiring  battery  can 
then  be  connected  to  the  core  or  not  as  desired.  If  it  be  not  connected 
a  positive  current  from  the  weak  current  battery  releases  the  armature, 
by  opposing  the  polarity  induced  in  the  electro-magnet  cores  l)y  the 
permanent  magnet,  and  brings  the  circuit-closing  apparatus  back  to  its 
normal  condition. 

This  circuit-closer  can  be  used  in  connection  with  automatic  firing 
apparatus  on  shore,  so  that  a  tiring  })attery  common  to  a  number  of 
groups  of  mines  is  automatically  switched  to  the  core  leading  to  the 
mine  which  is  struck  ;  but  this  leads  to  complications  and  difliculties, 
and  a  non-automatic  system  will  probably  be  found  to  work  more  satis- 
factorily and  in  a  simpler  manner.  Moreover,  automatic  firing  is 
almost  put  out  of  court  by  countermining. 

So  much  attention  has  been  devoted  to  the  systematic  attack  of 
niinetieldsin  this  manner,  that  some  form  of  retardation  in  the  circuit- 


126 


Suhmarine  Mining. 


closer  is  necessary,  because  these  instruments,  whether  they  can  retard 
or  not,  generally  signal  at  distances  considerably  greater  than  those  at 
which  their  cases  would  be  damaged.  The  operator  on  shore  should 
therefore  be  able  to  fire  a  mine  after  the  first  signal,  and  when  he  has 
become  assui'ed  that  such  signal  is  not  caused  by  a  countermine. 
Moreover,  vessels,  even  so  long  ago  as  the  American  War  of  Secession, 
endeavoured  to  procure  immunity  from  contact  mines  by  submei-ged 
strikers  rigged  out  in  front  of  their  l)0ws  to  produce  premature 
explosions. 

But  it  is  not  absolutely  necessary  that  the  retardation  should  be 
produced  by  an  electrical  combination.  It  will  probably  be  found 
that  the  arrangements,  especially  those  in  the  firing  station,  will  be 
simplified  by  the  employment  of  a  circuit-closer  with  a  mechanical 
retardation,  and  an  apparatus  of  this  description  has  recently  been 
designed  by  the  author. 

It  consists  of  his  ball-and-string  arrangement,  placed  in  a  cylindrical 
chamber  about  3|-  in.  diameter  and  high,  the  string  actuating  a  rod  R, 
Fig.    62,   which   carries  a  spi'ing  and  contact  maker  C,   which  when 


drawn  upwards  slides  ujinn  m  pl.il  iniMd  ,111  fur  P,  in  conn(X'tion  with 
the  terminal  F,  from  wiiich  is  led  the  wire  to  the  fuzes.  0  is  con- 
nected to  the  line  wire  at  L,  and  the  contact  is  prolonged  far  beyond 
the  period  occupied  by  the  oscillations  of  the  ball  B,  by  the  following 
device  :  The   lower  end  of  the  rod   R  carries  a  piston,  working  in  a 


Gircvbit-Glosers.  1 27 

small  cylinder  full  of  glycerine  or  other  suitable  liquid,  the  packing 
being  a  chamber  full  of  cotton  wool  W,  screwed  into  the  top  of  the 
cylinder.  The  piston  is  kept  in  its  normal  position,  and  any  slack  taken 
out  of  the  string  by  a  small  helical  spring  S,  working  on  the  rod  R,  and 
abutting  against  the  bottom  of  tlie  chamber  W.  The  piston  is  fitted 
with  four  or  more  valves,  each  opening  downwards  and  kept  normally 
closed  by  a  small  spiral  spring,  acting  on  each  valve  spindle  and 
abutting  against  a  small  crooked  crossbar  as  shown  in  Fig.  G2. 

When  the  buoy  or  case  carrying  this  circuit-closer  is  struck,  the  ball 
is  thrown  to  one  side  by  its  inertia,  the  string  is  pulled  through  the 
guide  hole,  the  valves  open,  and  the  piston  rises,  giving  contact  at  C. 
The  valves  now  close,  and  the  glycerine  has  to  leak  past  the  piston 
while  the  spiral  spring  S  gradually  pushes  it  downwards.  While  this 
is  going  on  the  operator  on  shore  can  fire  the  mine  if  desired.  The 
duration  of  the  retardation  can  be  adjusted  to  any  required  period 
by  the  space  allowed  between  the  piston  and  cylinder,  and  in  settling 
this  it  will  be  useful  to  remember  that  a  speed  of  6  knots  an  hour  is 
equivalent  to  10  ft.  per  second,  and  that  a  vessel  300  ft.  long  would, 
at  this  speed,  take  30  seconds  to  pass  any  given  point.  Even  at  18  knot 
speed,  10  seconds  would  be  occupied,  thus  giving  an  operator  plenty  of 
time  to  act  with  deliberation  and  discretion 

Mercurial  Contact  Circuit-Closer. — Circuit-closei's  in  which  contact 
is  made  by  the  movement  of  mercury  due  to  its  inertia  when  the  mine 
is  struck,  have  been  successfully  applied.  The  idea  was  first  brought  to 
the  notice  of  our  Government  in  1874  by  Captain  C.  A.  McEvoy,  who 
has  also  invented  several  other  circuit-closers  on  the  inertia  principle. 
They  form  a  simple  apparatus  for  mines  which  are  not  required  to 
remain  down  a  long  time.  When  stores  are  improvised,  the  mercurial 
form  of  circuit-closer  can  be  recommended;  but  it  is  most  diflicult  to 
prevent  a  scum  of  oxide  forming  on  the  mercury,  which  may  be  thrown 
upon  and  then  adheres  to  surfaces,  thei-eby  permanently  bridging  the 
electrical  break  in  the  circuit. 

The  apparatus  may  be  made  as  follows  :  Cut  2^  in.  from  a  i  in. 
iron  pipe ;  close  one  end  with  a  metal  plug  ;  thread  the  other  end  in- 
ternally ;  screw  a  wooden  cork  into  it ;  bore  a  hole  centrally  in  the 
cork;  cut  If  in.  from  a  No.  11  B.W.G.  wire;  thread  it  lightly  end  to 
end ;  fill  the  pipe  one-third  full  with  pure  mercury  ;  screw  the  wire 
through  the  cork  until  the  end  of  wire  is  about  its  own  diameter  from 
the  surface  of  the  mercury  ;  add  a  screw  terminal  on  that  portion  of  the 
wire  projecting  above  the  cork  and  the  circuit-closer  is  made. 

Contrivances  have  been  designed  to  protect  mercurial,  as  well  as 
other  forms  of  circuit-closers  acting  by  the  inertia  principle,  from  the 
shocks  of  countermines,  which  are  said  to  act  upon  buoyant  bodies  in  a 


128  Submarine  Mining. 

vertical  direction.  But,  assuming  this  to  be  the  case,  it  is  evident  that 
tlie  contrivances  must  fail  to  act  in  the  desired  manner  when  the  circuit- 
closers  are  out  of  the  vertical  themselves,  the  cases  containing  them 
being  tilted  by  tidal  currents  or  otherwise.  It  is  consequently  prefer- 
able to  protect  the  mines  from  self-destruction  caused  ])y  countermining, 
in  some  manner  that  will  act  efficiently  under  all  conditions. 

It  should  be  noted  that  a  mercurial  circuit-closer  does  not  and  cannot 
be  made  to  retard  either  mechanically  or  electrically.  On  the  whole, 
therefore,  it  must  be  regarded  as  decidedly  inferior  to  those  patterns 
examples  of  which  have  been  previously  described  in  these  pages. 

Wire  Entrances  to  Cases. — The  electric  wires  can  be  carried  into  the 
case  of  a  circuit-closer  buoy  or  mine  by  means  of  an  arrangement  very 
similar  to  that  already  depicted  in  Fig.  37,  page  74,  and  which  it  is  not 
necessary  to  describe  again. 

Disconnecting  Arrangements /or  Electro-Contact  Mihps. — The  discon- 
necting arrangements,  already  referred  to  on  page  116,  should  be  as 
simple  as  possible. 

Each  branch  cable  to  an  electro-contact  mine  should  pass  through  a 
disconnecting  fuze  placed  in  a  water-tight  case  in  the  junction  'box. 
When  a  group  of  these  mines  gets  out  of  order  it  is  necessary  to  raise 
the  junction  box  and  discover  the  fault,  which  may  exist  either  in  the 
core  leading  to  the  group  junction  box,  or  in  one  of  the  branch  cables 
or  mines.  Having  raised  the  box,  facilities  should  exist  for  testing  each 
of  these  cores  in  succession,  and  this  testing  is  generally  done  most 
conveniently  from  the  firing  station ;  signals,  electric  or  "visual,  passing 
between  the  operator  on  shore  and  the  party  in  the  junction  box  boat. 

When  the  mines  are  connected  up  on  the  fork  system,  it  is  necessary 
to  provide  a  disconnector  for  each  branch  cable  interposed  between  the 
cable  and  the  mine.  This  can  be  done  by  placing  a  disconnector  in 
a  specially  large  connecting  box  on  the  branch  cable  and  close  to  the 
sinker  of  each  mine.  But  it  is  far  better  to  place  all  the  disconnectors 
in  the  junction  box.  Various  devices  have  been  tried  for  combining  the 
several  disconnectors  into  one  apparatus  forming  part  of  a  special  junc- 
tion box,  and  for  combining  a  commutator  therewith  wliich  can  be 
plugged  or  unplugged  when  the  box  is  lifted  and  opened,  so  that  tests 
may  Ije  taken  from  shore  to  each  mine.  Also  an  apparatus  has  been 
pi'oposed,  and  I  believe  patented,  for  electrically  actuating  such  a  com- 
mutator from  the  shore,  and  thus  testing  daily  each  electro-contact 
mine  in  turn.  Those  shore  tests  will  not  rectify  a  fault,  and  a  simple 
resistance  test  for  tlie  whole  gi'oup  indicates  with  sufficient  clearness 
whether  a  group  box  should  be  laiscd  and  a  group  examined.  The 
more  complicated  tests  tell   us   very   little   more,   and    the   additional 


Single  Disconnector. 


129 


apparatus  are  liable  to  derangement.  The  first  step  to  be  taken  for  the 
recovery  of  a  faulty  mine  or  cable  is  tlie  raising  of  the  junction  box, 
and  no  important  economy  of  time  is  effected  by  localising  the  fault 
beforehand.  On  the  whole  it  is  better  to  have  a  separate  case  for  each 
disconnecting  fuze,  and  the  arrangement  shown  on  Fig.  63  (now  de- 
signed) would  act  efficiently. 


Fig.  63. 

The  upper  cylinder,  containing  the  india-rubber  plug  c,  siiould  Ije 
turned  out  internally,  but  the  rest  of  the  case  may  remain  rough  cast. 
The  gear  consists  of  an  ordinary  screw  bolt  working  through  a  cross- 
bar, supported  by  two  side  links  b  from  an  encircling  ring  d  slipped 
over  the  case  as  far  as  its  smaller  diameter  is  carried.  The  screw  bolt 
squeezes  the  india-rubber  plug  c  between  the  two  iron  plates,  thus 
forming  a  water-tight  joint  for  the  wire  entrance  to  the  chamber 
containing  the  disconnecting  fuze  e.  These  apparatus  being  carefully 
made  up  on  shore,  should  never  require  to  be  opened  on  the  mine  Held, 
where  one  leg  is  connected  by  an  insulated  joint  to  the  branch  wire 
leading  to  a  mine,  and  the  other  leg  to  the  core  of  the  single  group 
cable.  But  this  gives  no  facility  for  rapid  testing.  For  this  purpose  a 
multiple  connector  of  some  sort  should  be  interposed  between  the 
disconnectors  and  the  group  cable,  and  it  should  be  so  arranged  that  it 
can  be  easily  opened,  without  distui-bing  any  electrical  joint,  and  each 
branch  cable  or  the  group  cable  tested.  The  apparatus  shown  in 
Fig.  64  is  now  designed  by  the  writer,  and  will  serve  as  an  example  of 
what  is  required.  The  cylindrical  case  is  open  at  each  end  and  has  an 
internal  shoulder  near  one  end  against  which  a  wooden  disc  /al)uts.  A 

K 


130 


Submarine  Mining. 


water-tight  joint,  similar  to  one  just  descriljed,  is  formed  l)y  tlie  rubber 
plug  g,  the  iron  plate  h,  and  the  bolt  and  crossbar  i.  The  wires  from 
the  group  cables  and  the  wire  from  the  main  core  are  led  through  and 
connected  to  brass  terminal  screws  e  e  secured  in  the  top  of  the  wooden 
disc.  This  portion  of  the  apparatus  need  not  be  opened  on  the  mine 
field.  The  upper  end  of  the  cylinder  is  closed  by  a  rubber  ring  c,  a 
cover  b,  and  a  crossbar  with  screw  bolt  a.  The  brass  terminals  are 
provided  with  additional  screws  whereby  a  thin  piece  of  sheet  brass  is 
connected  to  all  from  the  central  terminal,  which  is  slightly  higher  than 
those  around  it.  Consequently,  when  the  binding  screws  that  secure 
the  sheet  brass  to  the  latter  are  released,  the  brass  will  spring  up  and 
be  out  of  contact  with  them.     Plugs  are   liable  to   be  shaken  out  hy 


Fiq£4 


noighbouring  explosions,  and  should  not  be  used.  An  earth  plate  over 
side  of  boat  can  then  be  connected  with  the  central  terminal,  and  the 
core  to  firing  station  tested  for  resistance.  If  good,  the  earth  plate 
wire  is  removed,  and  each  branch  cable  terminal  screwed  down  in  turn, 
and  the  several  resistances  tested  from  shore.  As  soon  as  the  faulty 
cable  is  found,  it  should  be  disconnected  from  the  junction  box,  under- 
run,  and  tlie  mine  picked  up,  taken  ashore,  and  the  defect  discovered 
and  made  good. 

The  general  arrangement  in  the  group  junction  box  is  shown  in 
Fig.  66  (the  section  is  sijuilar  to  that  shown  in  Fig.  51,  page  106,  and 
the  electrical  joints  between  the  seven  single  disconnectois  and  (lu' 
multiple  connector  may  be  made  on  shore,  and  if  done  carefully  sluiuld 
never  require  to  bo  touclied  again  on  the  mine  iicld. 


Multiple  Disconnector  and  Junction  Bo.i 


131 


The  nuinlxn-  of  mines  on  one  gi-oup  cable  depends  upon  tlie  electrical 
system  employed.  When  the  simple  arrangements  advocated  in  these 
pages  are  adopted,  each  mine  when  perfect  testing  infinity,  any  numher 
of  mines  can  theoretically  be  connected  in  one  group,  but,  us  one  faulty 


Fix).  66. 


mine  or  cable  destroys  the  ctHciency  of  the  group  for  the  time  the  fault 
lasts,  it  is  better  to  limit  the  number  of  mines  to  six  or  seven.  In  the 
English  service,  when  Colonel  Armstrong's  testing  apparatus  is 
employed  in  each  mine,  the  number  in  a  group  has  to  be  still  further 
restricted. 

It  will  now  be  convenient  to  examine  the  electrical  arrangements 
which  are  required  on  shore  for  controlling  and  firing  the  mines,  &c., 
that  have  been  described. 


k2 


132 


CHAPTER  XI. 

Electrical  Arrangements  on  Shore. 

Electro-Contact  Mines. — Continuing  with  electro-contact  mines,  the 
sea  arrangements  for  which  have  just  been  explained,  the  first  and  most 
important  thing  on  shore  is  the  firing  battery. 

It  is  a  matter  for  serious  consideration  whether  a  small  dynamo 
driven  by  hand  should  not  be  employed  for  the  purpose,  rather  than 
a  voltaic  battery.  For  the  arrangements  hereinbefore  recommended, 
as  the  group  mines  may  perhaps  be  as  far  off  as  three  sea  miles,  the 
external  resistances  may  be  108  ohms  for  cable  core,  2  ohms  for  two 
earths,  4  ohms  for  four  fuzes,  or  a  total  of  114  ohms.  The  minimum 
firing  current  being  0.17  ampere,  the  current  used  should  be  0.5  ampere 
(top  page  116).  Consequently  the  dynamo  should,  at  the  speed  driven, 
be  aUle  to  produce  a  current  of  0.5  ampere  through  an  external  resist- 
ance of  114  ohms. 

Following  the  beaten  track,  however,  the  best  voltaic  battery  to  use 
for  such  a  purpose  is  that  known  as  the  Leclanche,  with  an  electro- 
motive force  per  cell  of  1.45  volts,  and  the  cell  usually  employed  and 
specially  manufactured  for  the  purpose,  has  an  internal  resistance  of 
about  0.3  ohm.  But  the  fuze  which  it  is  now  proposed  to  employ  has  a 
resistance  of  1  ohm,  and  the  current  required  being  0.5  ampere,  such  a 
fuze  on  short  circuit  would  not  require  so  large  a  cell.  Thus,  if  the 
internal  resistance  of  the  cell  were  1  ohm  instead  of  0.3,  it  would 
possess  ample  power  and  would  give  a  current  through  a  1-ohm  fuze  on 
short  circuit  of  1.45 -^(l -1-1)  =  0.725  ampere.  A  Leclanche  firing  cell 
with  1  ohm  resistance  is,  therefore,  recommended  when  the  mines  are 
fired  by  fuzes  as  sensitive  as  those  now  employed  by  the  Royal  Engi- 
neers for  land  service. 

With  114  ohms  external  resistance,  if  N  be  tlie  number  of  cells 
recjuircd  in  battery, 

0.5=  1.45  N-f(N  + 114)  .-.  N  =  50  cells. 
But  the  mines  are  not  usually  so  far  ofi",  and  perhaps  one  mile  may  be 
taken  as  an  average  distance  in  most  harbours. 

The  external  resistance  then  =  42  ohms,  and  the  equation  becomes 
0.5=  1.45  N-r  (N-;  42) .  ■.  N  =  19  cells. 


Flrinfj  Battery.  1 33 

For  Distances  over  1000  Yards  if  D  be  the  Distance  in  Yards, 
N  =  D-f  1000  (nearly). 

"  The  Silvertown  firing  battery,"  Leclanche,  "  is  put  up  in  stout  boxes 
containing  ten  cells  coupled  permanently  in  series  witli  two  terminals 
outside.  Each  cell  is  sealed,  and  contains  all  the  parts  needful  for 
action  except  water,  which  is  to  be  introduced  through  two  holes  in  the 
top  introduced  for  the  purpose.  The  cells  are  made  of  ebonite.  The 
zinc  plate  ...  is  a  cylinder  .  .  .  surrounded  with  a  packing  of  sal- 
ammoniac  in  powder,  enough  being  inserted  to  more  than  saturate  the 
charge  of  water  .  .  .  Tlie  negative  element  in  its  present  agglomerate 
form  consists  of  a  central  carbon  hexagon  grooved  on  each  side  to  fit  a 
cylinder  of  compressed  peroxide  of  manganese  and  carbon,  6  in.  long 
and  .9  in.  in  diameter.  The  whole  are  wrapped  with  a  strip  of  burlap 
held  in  place  by  a  couple  of  rubber  bands.  Each  cell  is  4  in.  in 
diameter  and  7|  in.  high,  and  should  receive  about  eight  fluid  ounces  of 
water  when  the  battery  is  removed  from  store  for  use  in  service."  .   .   . 

"  Tlie  great  fault  of  the  arrangement  is  the  insertion  of  the  powdered 
sal-ammoniac  ;  but  the  sealing  is  also  a  defect.  The  salt  contains 
sufficient  moisture  to  slowly  encrust  the  zinc  with  a  coating  of  oxy- 
chloride  crystals,  which,  being  insoluble  in  the  added  water,  increases 
the  internal  resistance  much  above  its  normal  value.  To  remove  these 
incrustations  it  is  best  to  cut  through  the  pitch  covering,  take  out  and 
wash  the  zincs  in  a  strong  mixture  of  muriatic  acid  and  water,  re- 
amalgamate  them,  and  replace  them.  .  .  .  The  cells  should  never  be 
resealed.  Two  bits  of  marline  saturated  in  paraffin  and  packed  "... 
on  either  side  of  the  zinc  "  sufficiently  prevent  evaporation,  and  are 
far  more  convenient  than  the  pitch  cover.  The  cells,  when  required 
for  use,  should  be  charged  with  a  saturated  solution  of  sal-ammoniac, 
with  a  little  of  the  salt  added  to  supply  consumption,  the  zincs  being 
first  re-amalgamated."  ...  "A  firing  battery  of  forty  of  these  cells 
was  set  up  .  .  .  and  kept  in  active  service  for  over  six  years  "  (Abbot). 
As  before  stated,  the  internal  resistance  of  the  cell  above  described  is 
.3  ohm,  and  for  the  fuzes  now  recommended  a  resistance  of  1  ohm  is 
permissible.  A  cell  of  smaller  dimensions,  or  one  of  simpler  construc- 
tion, may  therefore  be  employed,  and  the  cell  recently  patented  by 
M.  Leclanclit?  will  possibly  be  found  to  answer  well.  This  arrangement 
is  illustrated  by  Figs.  67  and  G8,  and  consists  of  an  outer  glass  jar  A 
containing  an  exciting  solution  of  chloride  of  ammonium,  or  an  acid  or 
alkali,  in  which  is  immersed  a  central  cylinder  D  of  zinc.  The  positive 
electrode  is  formed  by  an  outer  hollow  cylinder  B  of  special  depolarising 
composition.  The  part  of  this  cylinder  which  is  above  the  solution  is 
paraffined,  and  has  a  ring  E  of  lead  or  other  metal  firmly  secured  to  it. 


134 


Stihmarine  Mining. 


The  cylinder  B  is  also  provided  witli  lioles  I  to  allow  free  passage  to  the 
exciting  liquid.  The  cylinder  D  is  kept  in  place  by  a  stopper  F  of 
wood  or  ebonite.  A  caoutchouc  ring  G  prevents  evaporation  of  the 
liquid.  The  cylinder  B  is  composed  of  a  mixture  of  peroxide  of  man"-a- 
nese,  graphite,  pitch,  and  sulphur,  moistened  with  water,  and  pressed 
into  shape  while  cold  and  then  baked.  The  operation  of  baking  induces 
partial  volatilisation  and  vulcanisation  of  the  composition,  which  is 
thereby  rendered  porous  and  a  good  conductor  of  electricity. 

Electro-contact  mines  not  fitted  with  testing  apparatus  can,  if  they 
are  all  in  good  order,  be  connected  direct  to  the  firing  battery.  But 
there  are  several  objections  to  such  a  proceeding  :  1.  It  is  peculiarly 
vulnerable  to  attack  by  countermines.  2.  A  number  of  mines  are  very 
rarely  "all  in  good  order."  3.  Boats  and  steamers  connected  with  the 
defence  may  accidentally  come  in  contact  with  the  mines.  4.  The  mines 
may  signal  by  wave  action.  5.  Some  of  the  mines  may  drag  their 
moorings,  and  the  explosion  of  one  mine  may  then  cause  others  to  signal 
and  be  exploded. 

t.  ^ 

%  6-5.      I"- 


Fir/.  67. 


For  these  and  other  reasons  the  tiring  battery  should  not  be  connected 
direct  to  lino,  and  it  becomes  necessary  to  devise  some  simple  arrange- 
ment of  apparatus  for  employment  in  the  firing  station,  so  that  the 
mines  may  be  under  control,  and  act  when  and  how  desired,  and  then 
and  thus  only.  If,  in  addition,  the  apparatus  so  employed  give  a  record 
of  the  number  of  mines  fired  in  each  group,  so  much  the  better. 

'J'hc  plan  usually  pursued  is  to  place  a  small  electric  current  con- 
tinuously on  "line,"  and  when  the  circuit-closer  in  or  above  the  sea 
mine  is  actuated  by  a  passing  vessel,  or  by  a  countermine,  this  current  is 
increased  by  a  decrease  of  circuit  resistance,  so  that  an  clocti'o magnet 
on  shore  moves  an  armatui'c  and  a  (lr(ii>i)ingsliu(ter,  wliich  .lutoniatically 
closes  the  firing  circuit,  rings  a  Ih'II,  S:r. 

Such  an  a)i])aratus  is  sliown  in  Fig.  (ID,  which  was  one  of  iMathieson's 


Signalling  and  Firing  Apparatus.  135 

first  designs  for  a  shutter  apparatus,  except  that  I  now  add  a  Ijtll 
circuit  and  spring ;/  for  same.  The  more  intricate  apparatus  since  elabo- 
rated for  the  Englisli  service  cannot  beat  tliis  simple  first  form. 

Plugs,  not  shown  on  Fig.  69,  should  be  provided  for  disconnecting  the 
batteries  S  B  and  R  B,  as  also  the  leading  wire  L  from  each  shutter  axis. 

An  armature  a  pivots  on  p  between  the  two  horns  6  6  of  an  electro- 
magnet, small  ivory  studs  preventing  actual  contact  between  them. 
The  lever  of  a  weighted  shutter  (No.  4)  engages  the  lower  end  of  the 
armature,  so  that  when  the  armature  is  attracted  by  the  electro-magnet 
the  shutter  falls.  This  occurs  when  the  resistance  of  line  is  decreased 
by  a  contact  made  at  the  circuit-closer  in  one  of  the  mines  of  the  groups 
connected  to  L.  The  axis  of  the  shutter  is  insulated  and  connected  to 
L,  and  the  metal  crossbar  e  is  normally  in  contact  with  the  spring  d. 
As  soon  as  the  shutter  falls  d  is  automatically  disconnected,  and  the 
firing  battery  F  B  is  connected  direct  to  L  through  the  spring  /  if  the 
firing  plug  P  has  been  inserted.  In  general  a  small  bell  is  struck 
mechanically  by  the  falling  shutter.  But  I  prefer  to  employ  a  ring 
bell  on  a  local  circuit  arranged  as  shown  in  Fig.  69.  This  arrangement 
does  not  affect  the  firing  battery,  although  the  firing  battery  spring  is 
used  for  it.  The  wires  WW  lead  to  the  springs  g f  oi  the  other 
shutters.  The  signalling  battery  S  B  can  be  common  to  the  seven  appa- 
ratus in  one  set.  The  firing  battery  F  B  and  the  releasing  battery  R  B 
can  be  common  to  a  number  of  sets.  A  releasing  battery  is  of  course 
only  required  when  a  circuit-closer  is  used  that  can  retard.  Mathieson's 
shutter  apparatus  was  designed  about  the  year  1870,  and  has  been 
employed  in  our  service  in  a  modified  form  ever  since.  'An  apparatus 
was  patented  by  Captain  McEvoy  in  1884,  by  which  similar  actions 
were  produced  by  a  shutter  falling  between  guides  ;  but  the  pendulum 
action  is  preferable,  as  it  is  less  likely  to  be  aflfected  by  the  concussions 
due  to  the  firing  of  heavy  artillery,  and  the  axis  of  the  pendulum  motion 
affords  a  more  reliable  method  of  changing  the  connections. 

If  the  circuit-closing  arrangement  in  the  sea  be  made  to  retard  either 
magnetically  or  mechanically,  the  firing  battery  can  be,  and  generally 
is,  plugged  after  the  shutter  falls,  and  in  this  manner  the  self-destruc- 
tion of  sea  mines  by  the  concussions  caused  by  countermines  may  be 
obviated,  means  being  provided  to  acquaint  the  operator  with  the 
operations  that  are  proceeding  in  the  water. 

Tlie  current  required  to  actuate  such  an  automatic  system  cannot  be 
much  less  than  0.15  ampere  (American  system,  Abbot),  and  the  fuzes 
employed  should  therefore  not  fire  with  less  than  x/10  (0.15)' or  0.47 
ampere.  The  firing  current  to  insure  simultaneous  ignition  of  fuzes  in 
mine   and    disconnector   should,    therefore,   be   1   ampere.     A   shutter 


136  Submarine  Mining. 

apparatus  may  be  accidentally  actuated  by  the  concussions  produced 
by  the  discharge  of  large  guns  in  its  \dcinity,  unless  care  be  taken 
to  guard  against  it.  Again,  the  development  of  the  attack  of  sea 
mines  l)y  countermining  almost  prohibits  the  use  of  a  purely  auto- 
matic method  of  firing,  and  if  we  are  never  to  use  the  shutter 
apparatus  in  this  manner  there  is  nothing  to  recommend  it  in  pre- 
ference to  simpler  arrangements  that  depend  upon  the  vigilance  of  an 
operator.  In  designing  such  an  arrangement  it  is  of  the  utmost  im- 
portance to  remember  that  the  number  of  highly  trained  electricians 
available  in  time  of  war  may  be,  and  probably  will  be,  limited.  If, 
therefore,  tlie  arrangments  can  be  worked  by  men  of  ordinary  intelli- 
gence, by  following  some  simple  and  clear  instructions,  a  great 
advantage  will  be  gained.  Many  arrangements,  much  simpler  than 
those  now  in  vogue,  can  no  doubt  be  elaborated,  and  the  following  is 
given  as  an  example.  It  has  been  designed  by  the  writer  as  he  penned 
these  pages,  and  appears  to  be  a  simple  solution  to  the  proljlem. 
Advantage  has  been  taken  of  the  theory  of  the  simultaneous  ignitions 
of  low-resistance  fuzes  already  explained. 

About  two  years  ago  a  naval  officer  in  the  Vernon  Torpedo  School 
brought  to  my  notice  the  advantageous  use  of  what  he  termed  a  protect- 
ing fuze  in  the  firing  station.  His  idea  was  to  use  one  such  fuze  and 
replace  it  when  expended.  I  now  propose  to  enlarge  upon  this  idea, 
and  to  place  a  number  of  such  fuzes  systematically  on  the  firing  bar, 
one  for  each  mine,  and  to  plug  each  in  rotation  in  every  group  of 
mines. 

The  firing  of  each  fuze  will  then  not  only  "  protect  "  the  remainder 
of  the  mines  in  that  group  from  premature  and  undesired  explosion, 
but  will  also  indicate  that  a  mine  has  fired,  and  remain  as  a  lasting 
indication  thereof. 

Let  us  assume  that  the  mine  fuzes  have  a  firing  current  sensitivity  of 
about  0.17  ampere,  and  that  they  are  placed  out  of  circuit  until  tlie 
circuit-closer  is  actuated,  as  described  in  the  recent  chapter  on  circuit- 
closers.  Also  that  the  latter  are  provided  with  a  magnetic  retardation 
releasable  at  will  by  a  suitable  current  from  the  firing  station,  or  with 
a  mechanical  retardation  lasting  for  several  seconds  before  the  circuit  is 
again  opened  at  tlie  circuit-closer.  As  many  as  seven  mines,  and  e\en 
more,  can  then  be  placed  on  each  cable  core  (see  plan  of  mine  field  on 
sketch.  Fig.  70).* 

Each  core  is  led  througli  a  discoiinci-ting  fuze  ,uk1  a  iiiuUipli'  coii- 
nc^ctor  in  the  group  junction-box  (Roman  figures  on  plan)  to  the  firing 

*  lu  this  figure  the  scale  above  X  Y  is  about  1  in  1000,  and  below  X  Y  it  is 
about  1  in  8. 


Apparatus,  Fuze  [ndioafivg. 


137 


138  Submarine  Mining. 

station,  wliere  tlie  path  is  split,  tbe  road  to  the  firing  battery  passing 
through  another  disconnecting  fuze  to  the  firing  bar,  and  thence 
through  one  of  my  patent  (pull)  contact-makers  C  M  to  the  negative 
pole  of  the  firing  battery  F  B  and  "  earth,"  C  M  being  normally 
open,  and  the  other  route  passing  through  a  disconnecting  fuze  to  the 
signal  battery  bar,  and  thence  through  a  galvanometer  and  one  of  my 
patent  (pull)  circuit-breakers  C  B  to  the  signal  battery  S  B  and  "  earth." 
C  M  and  C  B  are  actuated  simultaneously  by  a  pull  on  the  cord  from 
the  handle  H.  By  pulling  this  handle  and  securing  it  on  the  peg  P, 
the  arrangement  becomes  automatic.  With  magnetic  retardation 
requiring  a  positive  releasing  current  the  employment  of  a  separate 
releasing  battery  can  be  avoided  by  sending  a  reversed  current  from 
the  signalling  battery  to  line.  This  can  readily  be  done  as  indicated 
on  sketch  by  the  employment  of  two  of  my  contact-makers  and  two  of 
my  contact-breakers  actuated  by  one  pull  cord  and  handle  K,  the  con- 
nections being  made  as  shown  in  Fig.  70.  The  tests  for  resistance  of 
each  may  be  taken  daily  (and  perhaps  oftener),  group  by  group,  without 
interfering  with  the  signalling  and  firing  arrangement  of  the  other 
groups  if  the  wires  and  plugging  plates  be  arranged  as  indicated,  the 
plug  S  and  the  plug  to  firing  bar  being  removed  from  any  group  which 
is  to  be  tested,  and  the  wandering  lead  T  inserted  in  plug-hole  T  of  that 
group.  The  apparatus  recommended  for  this  test,  and  shown  on  the 
plan,  consists  of  a  battery,  galvanometer,  key,  and  a  set  of  eoik  with 
bridge  which  is  capable  of  testing  resistances  from  j^L  ohm  to  11,000 
ohms,  an  ample  range  for  all  sea  mine  purposes.  The  whole,  including 
battery,  is  contained  in  a  box  9  in.  by  6  in.  in  plan,  and  one  such  appa- 
ratus will  probably  be  enough  for  one  firing  station.  (Makers — Elliott 
Brothers,  London.) 

The  firing  battery  may  be  common  to  a  number  of  similar  arrange- 
ments in  one  firing  station.  Each  firing  station  should  be  provided 
with  an  electric  bell  under  the  control  of  an  observer  placed  so  as  to 
cdiiiinaiid  a  good  view  of  the  mined  waters  and  channels  of  approach, 
pi-oljably  at  one  of  the  stations  for  observation  firing.  He  would  then 
control  the  firing  of  both  the  observation  and  electro-contact  mines. 

This  observer  may  advantageously  be  connected  with  submerged 
telephones  so  that  tlie  explosion  of  countermines  may  be  detected  by 
him.  If  for  this,  or  other  cause,  he  considers  that  the  electro-contact 
mines  ^iiould  not  be  fired,  he  rings  the  caution  bell  in  tlie  liring 
station.  If  possible  he  should  be  in  telegraphic  coiinminic.it ion 
with  the  olficer  in  command  of  the  picket  boats.  AN'licii  tiie  caution 
bell  is  ringing  in  the  firing  station,  the  handle  H  must  imt  be  touclicd  : 
and  if  G  deflect  at  this  time  a  quick  luill  on  the  liaiuUc  l\  should  bring 
it  back  to  normal.     If  not,  this  pull  on  \\  shuukl  be   repi'atcd.     When 


Apparatus,  Fuze  Indicating.  139 

the  caution  bell  is  not  ringing  the  handle  II  must  be  pulled  when  G 
deflects.  This  should  life  a  mine,  also  one  or  the  indicating  and  pro- 
tecting fuzes,  thus  preventing  any  other  mine  in  the  group  being  fired, 
and  if  the  groups  be  separated  a  little  more  than  shown  on  diagram, 
no  fear  need  be  entertained  that  a  mine  in  one  group  will  cause  one  in 
another  group  to  explode.  As  soon  as  a  fuze  is  fired,  the  handle  H 
should  be  released,  and  if  G  still  deflect  a  pull  on  K  should  free  it. 
Another  fuze  should  then  be  plugged  to  the  firing  bar,  for  that  group. 

These  operations  are  simplified  when  mechanical  retardation  is  used 
in  the  sea  circuit-closers,  the  releasing  current  being  omitted,  ;iiul  ilio 
pull  handle  K,  &c. 

The  fuzes  when  fired  should  not  be  remo\ed.  They  then  form  a 
record  of  the  mines  expended. 

Faults. — Should  a  group  test  low,  a  faulty  branch  can  sometimes  be 
disconnected  by  the  firing  battery,  the  fault  then  being  beyond  a  group 
junction-box  disconnector.  A  fuze  should  fire  at  the  firing  station,  and 
the  deflection  on  G  go  to  normal  when  H  is  released.  Another  fuze 
can  then  be  plugged  to  the  firing  bar,  and  the  remaining  mines  of  the 
group  become  effective.  This  drastic  method  should  only  be  resoi-ted 
to  by  command  of  an  officer,  who  should  order  same  only  when  it  is 
more  important  to  have,  say,  six  mines  effective  at  once  than  seven  a 
few  hours  later.  If  repair  be  decided  upon,  the  faulty  group  must  be 
disconnected  from  the  system  by  unplugging  the  fuze  to  firing  bar  and 
removing  plug  S  of  the  group.  The  group  junction-box  must  then  be 
raised,  the  multiple  connector  opened,  the  wandering  lead  T  plugged  in 
the  plug-hole  T,  of  group  at  firing  station,  and  each  core  tested  as  before 
explained.  The  fault  should  then  be  rectified  by  laying  a  new  mine  or 
by  other  means,  and  the  group  efficiency  recovered. 

The  electromotive  force  of  the  voltaic  batteries  employed  in  this  ar- 
rangement being  low,  it  is  not  necessary  to  use  ebonite  for  insulating 
purposes.  The  plugging  brasses  can  therefore  be  secured  to  a  kiln-dried 
hard  wood  backing  protected  from  damp  by  hard  varnish.  Teak  is  pro- 
bably the  best  wood  to  employ,  certain  experiments  instituted  by  the 
United  Telephone  Company  having  given  the  following  comparative 
results  : 


Table  XXXII. ■ 

—Electrical  Rusistancks. 

Wood  op  8o: 

Mahogany, 

resistance,  comparative,  along  fibre 

40 

Pine 

214 

Rosewood 

,,              ,,              ,, 

eoi 

Beech 

:<!)7 

Oak 

478 

Teak 

,, 

7;u 

Resistances  across  fibre  are  from  50  to  100  per  cent,  greater. 


140  Siihmarhie  M'lvlng. 

The  firing  station  must,  of  course,  be  kept  dry  l)y  means  of  artificial 
heat. 

Insfructinns  for  Operator. 

Caution  Bell  Ringing. — G  deflects.  Pull  K.  Deflection  should 
vanisli.     If  not,  repeat. 

Caution  Bell  not  Hinging. — G  deflects  ;  pull  H.  A  fuze  should  fire. 
If  not,  repeat.  G  should  now  cease  to  deflect.  If  not,  pull  K,  and  this 
will  occur.     Plug  another  fuze  to  firing  bar. 

With  mechanical  retai'dation  the  pull  cord  and  handle  K  ai-e  omitted, 
and  the  instructions  are  still  simpler,  thus  : 

Caution  Bell  Hinging. — ^Do  nothing,  whether  G  deflects  or  not. 

Caution  Bell  not  Ringing. — G  deflects  ;  pull  H  ;  fuze  should  fire.  If 
not,  repeat.     G  ceases  to  deflect ;  plug  another  fuze  to  firing  bar. 

The  signalling  battery  employed  should  be  capable  of  working  con- 
tinuously on  a  somewhat  leaky  line.  A  single  fluid  gravity  Daniell  cell 
is  probably  the  best  suited  for  such  conditions.  To  avoid  any  possibility 
of  accidental  explosions  the  resistance  of  each  cell  should  be  such  that 
the  current  on  short  circuit  through  one  of  the  fuzes  employed  does  not 
exceed  0.054  ampere  (see  page  117).  Hence,  the  electromotive  force 
of  a  cell  being  1  volt,  and  the  fuze  resistance  (cold)  1.6  ohms,  if  x  be 
the  liquid  resistance,  we  have  0.054  =  1  ^(1.6 +  .t),  from  which  *•=  17 
ohms.  The  size  and  arrangement  of  each  cell  should  therefore  be  such 
that  it  possesses  this  amount  of  resistance. 

Looking  back  to  the  circuit -closer  recommended  for  magnetic  retar- 
dation (page  1 24  ),  it  will  be  seen  that  the  signalling  current  is  re- 
quired to  perform  no  work  except  moving  a  galvanometer  when  an 
electro-contact  mine  signals.  Retardation  is  effected  by  the  induced 
magnetism  from  the  permanent  magnet  holding  up  the  armature.  But 
the  releasing  current  has  to  perform  work,  viz.,  to  neutralise  the 
said  magnetism  in  order  to  produce  the  fall  of  the  armature.  The 
coil  in  the  circuit-closer,  the  strength  of  the  magnet,  and  the  size 
of  the  ivory  stops,  must,  therefore,  be  so  adjusted  that  a  current  of, 
say,  0.054  ampere  from  the  signalling  battery  reversed  will  act  as 
desired.  Assuming  that  this  adjustment  has  been  secured  by  the  in- 
strument maker,  the  number  of  cells  required  can  be  calculated.  Let 
the  line  fuzes,  eartlis,  and  circuit-closer  coil  amount  to  a  total  external 
resistance  of  80  ohms,  and  six  cells  will  be  the  number  required  in  the 
signalling  battery. 

The  battery  employed  for  tlie  resistance  tests  can  be  a  higli-resistance 
Leclanclid 

Large  Mines  provided  irilli  JMaclicd  Cirrnit-Cloi^rn^  can  bo  arranged 
in  a  precisely  similar  manner   if  they  mit  not  to   1h'  tired   liy  observa- 


Firing  Observation  Mines. 


141 


tion  as  wdII,  but  such  niiues  must  be  spaced  in  group,  so  that  they 
will  not  damage  one  another,  or  their  detaclied  circuit-closers  (see 
page  87). 

If,  tlierefore,  the  groups  be  spaced  so  that  the  explosion  of  a  mine  will 
not  signal  those  in  another  group,  the  system  now  recommended  enables 
us  to  place  such  mines  in  group  much  nearer  to  each  other  than  is 
possible  by  the  methods  of  shutter  apparatus  usually  employed.  Mines 
with  detached  circuit-closers,  arranged  for  purely  contact  iiring,  then 
become  a  formidable  defence  (page  78).  Hitherto  it  has  been  necessary 
to  space  them  so  far  apart  that  a  great  expenditure  of  cable  became 
necessary  in  connection  with  their  employment.  For  important  har- 
bours the  flanks  of  the  narrow  navigating  channels  may  therefore  be 
mined  in  future  on  the  plan  suggested.  The  experiments  against 
H.M.S.  Resistance,  and  the  provision  of  numerous  water-tight  compart- 
ments in  modern  war  vessels,  favour  the  employment  of  large  charges 
that  rack  and  shake  a  ship  from  stem  to  stern  rather  than  small 
charges,  which  are  far  more  local  in  etfect. 

The  employment  of  apparatus  whereby  large  charges  can  be  tired  either 
by  a  detached  circuit-closer  or  by  observation  has  already  been  alluded  to  on 
page  124.  Arrangements  of  the  kind,  giving  the  two  methods  of  ignition, 
are  old,  and  have  fallen  into  disuse  for  some  years.  They  produce  com- 
plications in  the  firing  arrangements,  and,  as  a  number  of  observation 
mines  must  be  used  in  the  channels  kept  open  for  traffic,  the  trained 
observers  available  at  any  one  port  are  likely  to  be  fully  employed  in 
working  them,  and  the  system  cannot  be  i-ecommended. 

Observation  Mines. — Firing  hy  Single  Observation. — Large  sea  mines, 
situated  near  to  an  observing  station,  are  sometimes  tired  by  one  ob- 
server when  a  vessel  is  between  marking  buoys  that  indicate  the  position 
of  the  mines.  When  this  plan  is  resorted  to,  several  mines  (three, 
four,  or  five)  are  usually  connected  up  in  one  line  and  fired  simulta- 
neously, the  marking  buoys  being  moored  near  to  the  extremities 
of  the  lines,  which  are  placed  across  the  channel.  Reverting  to 
Fig.  39,  page  79,  taking  the  beam  of  a  vessel  at  60  ft.,  and  the 
spacizig  between  the  mines  at  60  ft.  more,  or  a  horizontal  striking 
distance  for  each  mine  of  30  ft.,  it  will  be  seen  from  Table  XXIV., 
page  80,  that  the  strike  of  each  mine  should  be  39  ft.  for  40  ft.  depth  of 
water  at  high  tide,  42|-  ft.  strike  for  50  ft.  depth,  52  ft.  strike  for  60  ft. 
depth,  60  ft.  strike  for  70  ft.  depth,  68  ft.  strike  for  80  ft.  depth,  76  ft. 
strike  for  90  ft.  depth,  and  85  ft.  strike  for  100  ft.  depth. 

Charges  Jietjuired  at   Various  Depths. 
Comparing  these  figures  with  the  effective  striking  distances  of  the 


142  Submarine  Mining. 

mines  suggested  for  adoption  on  pages  83  to  86,  it  will  be  found  that 
the  small  ground  mine  loaded  with  gun-cotton  will  not  act  efficiently  in 
a  line  of  mines  spaced  at  120  ft.  intervals  even  at  so  small  a  depth  as 
40  ft.  Dynamite  can  be  used — not  because  it  is  stronger  per  pound, 
but  because  the  case  will  hold  a  heavier  charge,  giving  a  strike  of  45  ft. 
At  50  ft.  depth  the  same  mines  with  dynamite  or  stronger  explosive 
may  be  used.  If  gun-cotton  only  be  available  the  large  ground  mines 
must  be  used  at  depths  of  40  ft.  and  50  ft.  At  60  ft.,  the  small  ground 
mine  with  gelatine  dynamite  or  stronger  explosive  may  be  used.  At 
70  ft.  depth  the  small  ground  mine  with  explosive  gelatine,  or  the  large 
ground  mine  with  dynamite  or  stronger  explosive,  may  Ije  used.  At 
80  ft.  depth  the  large  ground  mine  with  dynamite  or  stronger  explosive 
may  be  used.  At  90  ft.  depth  the  large  ground  mine  with  gelatine 
dynamite,  or  stronger  explosive  may  be  used.  At  100  ft.  depth  the 
large  ground  mine  with  explosive  gelatine  is  required.  Above  100  ft. 
depth  either  the  large  or  the  small  buoyant  mine  may  be  used,  and  be 
loaded  as  desired,  the  submersion  being  regulated  accordingly. 

By  this  system,  a  line  of  two  mines  will  cover  180  ft.  of  cross  channel, 
three  mines  240  ft.,  four  mines  300  ft.,  and  five  mines  360  ft. 

When  it  is  desired  to  keep  a  still  wider  channel  than  360  ft.  open  for 
traffic,  and  therefore  clear  of  all  E.O.  mines  or  other  obstructions,  it  can 
be  done  by  providing  a  line  of  fairway  buoys  down  the  centre  of  the 
channel,  and  a  line  of  boundary  buoys  on  either  side  of  the  channel. 
One  half  channel  can  then  be  used  for  up  and  the  other  for  down  traffic. 
Lines  of  mines  can  be  placed  in  each  half  channel,  and  if  lines  of,  say, 
four  mines  each  be  used  the  total  width  will  be  600  ft.,  which  ought  to 
be  sufficient  even  for  the  Thames  or  Mersey.  This  is  perhaps  better 
than  providing  two  independent  and  separate  channels,  each  300  ft. 
wide,  because  the  traffic  vessels  could  keep  near  to  the  fairway  buoys, 
and  thereby  be  certain  not  to  damage  any  E.G.  mines  near  the  boundary 
lines. 

The  marking  ])uoys  should  be  distinguished  l)y  shape  rather  than 
colour,  because  colours  cannot  lie  seen  well  at  night,  whereas  the  electric 
light  brings  out  the  shape  of  any  object  with  clear  detinition,  especially 
if  it  be  painted  white  or  red. 

One  observer  can  look  after  three  or  four  lines  of  mines,  and  perhaps 
as  many  as  six  lines,  but  this  is  putting  too  many  eggs  in  one  basket. 
The  observer  should  have  an  assistant  (out  of  tire)  to  take  Ids  place  in 
the  event  of  a  casualty. 

There  are  other  methods  of  firing  by  single  observation  which  require 
the  observing  station  to  possess  a  good  command  (in  height)  over  the 
mined  waters.  The  camera  obscura  is  so  used  in  the  Austrian  service  ; 
but  it  fails  in  bright  moonlight,  when  the  picture  becomes  so  obscure 


Firivii  Observation  Mines.  143 

that  many  objects  seen  cloarly  with  tlio  naked  cyo  direct,  cannot  be 
distinguislied  upon  it.  Other  arrangements  for  tiring  mines  by  a  single 
observer  placed  some  distance  above  the  sea  level  have  been  made. 

One  of  the  first,  an  instrument  designed  by  Major  H.  S.  S.  Watkin, 
R.  A.,  was  a  development  from  his  well-known  depression  range  finder  ; 
but  was  complicated  by  springs,  chains,  pulleys,  etc.,  in  order  to  obtain 
the  movement  of  an  indicator  over  an  adjoining  chart,  which  represented 
the  mined  waters.  Another,  designed  by  the  writer,  had  an  arm  with 
terminal  pointer  connected  to  the  telescope  axis  by  elliptical  gearing, 
so  as  partially  to  counteract  the  reduction  of  scale  due  to  perspective,  and 
this  pointer  traversed  a  chart  pasted  on  a  nearly  spherical  surface  fixed 
behind  the  instrument  and  observer.  There  was  no  correction  for  rise 
and  fall  of  tide,  and  it  consequently  failed  in  most  situations.  Finally 
Major  Watkins  invented  an  excellent  instrument  of  comparatively 
simple  construction  which  has  been  adopted  for  employment  in  our 
service.     Unfortunately  this  instrument  cannot  be  described. 

The  theoretical  considerations  underlying  the  construction  of  all 
depression  instruments  that  possess  a  correction  for  alteration  in  tidal 
level    is    shown   on    Fig.    71,    where   A    C    represents   the   telescope's 


F19.7;. 


collimation,  B  0  the  horizontal  scale  employed,  D  E  the  water  surface, 
A  B  the  scaled  height  of  telescope,  A  D  its  actual  height  above  water 
level.  If  the  latter  be  altei-ed  to  D^  from  a  tidal  rise,  or  A  D  decreased 
to  A  D',  then  in  order  to  obtain  a  tidal  correction  in  the  instrument, 
A  B  must  be  proportionally  decreased  to  A^  B,  and  if  A'  and  E'  be 
joined  they  will  still  pass  through  C,  the  length  of  C  B  still  indicating 
the  distance  of  the  mine  E  from  the  vertical  A  D. 

The  inherent  defect  of  all  depression  instruments,  whether  for  finding 
range  or  for  plotting  the  positions  of  objects  on  a  chart,  consists  in  the 
difficulty  encountered  in  finding  visually  the  water  line  of  the  object 
observed. 

At  night  it  is  especially  difficult  to  see  the  water  line  of  a  black  hull 
moving  slowly  through  water  that  also  appears  to  be  black ;  and  if 
the  vessel  move  fast,  the  bow  wave  and  wave  of  depression  behind  it 
make  it  almost  impossible  to  discover  the  true  level  of  the  water  line. 


l-ii  Siihnarine  Mining. 

It  has  been  proposed  to  employ  depression  instruments  witli  a  command 
of  50  ft.  or  60  ft.,  say,  20  yards. 

With  such  a  command  an  error  of  one  vertical  yard  in  taking  the 
observation  causes  an  error  in  range  of  48  yards  at  1000  yards  if  the 
vertical  error  be  downwards,  and  of  52  yards  if  it  be  upwards.  As  the 
vessel  itself  is,  say,  20  yards  wide,  the  latter  error  would  be  reduced  to 
32  yards.  It  may  be  urged  that  the  cut-water  is  the  proper  point  to 
observe.  But  the  bow  wave  would  make  such  an  observation  un- 
reliable. Approximate  accuracy  can  only  be  obtained  by  using  one  of  the 
crosshairs  horizontally,  then  lining  it  with  the  water  line  on  the  vessel's 
side  nearest  to  the  observer,  and  thereby  obtaining  the  mean  or  average 
line  of  flotation.  Remembering  that  the  large  mines  cannot  con- 
veniently give  more  than  30  ft.  or  10  yards  radius  to  the  circle  of 
observation,  it  appears  evident  that  depression  instruments,  however 
perfect  in  themselves,  should  not  be  employed  when  the  command 
obtainable  does  not  exceed  60  ft.  At  what  command  can  their  employ- 
ment be  permitted  ? 

Assuming  that  the  instrument  must  be  efiective  at  night,  and  taking 
into  consideration  the  undeniable  fact  that  the  vessels  to  be  observed 
will  pi'obably  be  enveloped  in  smoke,  that  their  water  line  will 
frequently  be  invisible,  and  will  often  have  to  be  guessed  at  from  short 
glimpses  at  the  remainder  of  the  hull,  those  who  are  unbiassed  will 
agree  that  under  such  circumstances  a  vertical  error  proportional  to  1  in 
1000  of  range  is  likely  to  be  made  by  the  coolest  and  most  careful 
observer. 

Let  H  be  the  height  of  instrument  above  water  level  which  it  is 
desired  to  find. 

Let  D  be  the  horizontal  distance  of  the  mine  M  and  r  its  horizoutal 
distance  from  the  ship's  side  S  (see  Fig.  72). 


F15.72. 


iM 
Then  if  v  be  the  vertical   error  of  obsei'vation,   r  becomes  the  hori- 
zontal error,  and 

H  :  J)  :  :  r  :  r. 
But 

i;  =  D4-1000. 
Consequently 

H-D-'-flOOOr. 


Firing  hy  Depression.  145 

But  r  should  not  exceed  tlic  radius  of  horizontal  effect  of  the  mine. 
Consequently,  tlie  height  of  a  depression  instrument  should  not  be  less 
than  the  square  of  the  distance  in  yards  of  the  furthest  mine,  divided 
by  1000  times  the  horizontal  radius  of  effect  of  the  mine,  which  latter 
may  be  taken  at  10  yards  for  a  mine  charged  with  500  lb.  of  a  high 
explosive.     Thus : 

WhenD=   500  yards  H=   25  yards  =   75  feet 

D  =  1000     „  H=100     „     =300    „ 

D  =  1500    „  H  =  225     „     =675    ,, 

Depression  instruments  do  not  therefore  possess  sufficient  accuracy 
for  firing  mines  singly  during  the  smoke  of  an  engagement,  and  the 
high  value  claimed  for  this  system  of  firing  is  certainly  not  deserved. 

When  the  probable  course  of  the  vessel  of  a  foe  is  perpendicular  to 
the  line  of  sight  A  E,  Fig.  7 1 ,  two  or  more  mines  can  be  placed  on  one  core 
and  be  fired  simultaneously,  the  point  observed  being  the  centre  of  such 
a  group,  and  the  mines  being  each  moored  on  the  line  of  sight.  The 
spacing  of  such  mines  should  follow  the  same  rule  as  that  for  lines  of 
mines  between  marking  buoys,  already  given,  viz.,  120  ft.  Consequently 
the  width  of  channel  covered  by  a  pair  of  mines  would  be  180  ft.,  and  r 
in  above  proportion  becomes  180^2x3  yards -=30  yards,  instead  of 
10  yards,  and  the  height  of  the  depression  instrument  may  be  reduced 
accordingly.     Thus : 

WhenD=  500  yards  H=  25  feet 

D  =  1000      ,,  H=100   „ 

D=1500      „  H  =  225   „ 

These  figures  indicate  that  mines  in  pairs  should  generally  be  em- 
ployed in  connection  with  single  observation  instruments  working  by 
depression. 

The  great  defect  in  this  system  of  firing  mines,  viz.,  the  impossibility 
to  observe  the  water  line  of  a  vessel  when  she  is  enveloped  in  dense 
smoke,  is  not  shared  by  the  system  in  which  a  mine  is  fired  when  it 
coincides  with  the  intersection  on  plan  of  two  separate  lines  of  sight, 
because  the  mast  of  a  vessel  is  seldom  obscured  by  smoke.  Instruments 
for  firing  mines  by  the  intersection  of  lines  lying  on  the  horizontal 
plane  are  therefore  much  to  be  preferred.  Nevertheless,  the  fact  should 
be  recorded,  that  adepts  in  this  country  do  not,  as  a  rule,  share  this 
opinion,  and  for  several  years  firing  by  double  observation  has  therefore 
received  but  little  attention. 

Firing  by  Double  Observation. — Accuracy,  that  all-important  element, 
can  be  absolutely  assured  when  the  base  is  not  less  than  about  one- 
third  of  D,  the  distance  of  the  furthest  mine.  In  other  words,  the  angle 
of  intersection  should  not  be  less  than  20  deg.   This  can  always  be  easily 


146  Suhmarine  Mining. 

obtained  by  the  horizontal  intersection  of  two  lines  of  sight,  but  two 
separate  observers  are  required.  Instruments  have  been  designed  by 
whicli  quite  a  short  base  is  used,  and  the  two  observers  are  therefore 
placed  close  to  each  other.  It  is  quite  impossible  for  such  instruments 
to  work  with  sufficient  accuracy  to  fire  distant  mines  at  the  desired 
moment.  The  objection  to  firing  by  cross  intersection,  or  double  obser- 
vation, is  the  liability  of  the  two  men  to  observe  different  ships  or 
different  parts  of  the  same  ship.  But  the  employment  of  the  electric 
search  light  facilitates  matters  very  considerably,  a  rule  being  followed 
that  the  two  observers  shall  sight  on  that  vessel  which  is  illuminated  by 
the  ray  of  light,  and  stick  to  her  as  long  as  the  light  remains  upon  her. 
Also  a  rule  should  be  made  that  the  centre  of  the  foremast  shall  be  tJie 
point  of  observation ;  and  the  difficulty  is  reduced  to  a  minimum. 

The  observers  for  double  observation  firing  should  be  situated  at  some 
distance  from  the  smoke  of  a  battery,  and  would  probably  be  more 
secure  from  machine-gun  fire  when  placed  at  some  considerable  elevation 
above  the  mined  waters. 

Various  instruments  liave  been  elaborated  for  firing  by  intersection. 
One  of  the  first  arrangements  with  which  fairly  accurate  results  were 
obtained  up  to  ranges  of  1000  yards,  consisted  in  placing  a  number  of 
small  pickets  on  the  circumference  of  a  circle  about  20  ft.  radius,  a 
central  picket  giving  the  position  of  the  observer's  eye.  This  acts  well 
enough  as  an  improvised  arrangement,  when  the  instruments  for  obser- 
vation firing  have  been  damaged. 

If  the  space  required  be  not  available,  the  scale  can  be  reduced  by 
employing  a  flat  board  in  the  form  of  a  segment  of  a  circle,  and  placing 
small  sights  on  the  circumference.  Also,  if  desired,  the  centi-e  of  the 
segment  may  form  the  outer  sight,  and  the  eye  of  the  observer  be  placed 
at  each  of  the  inner  sights  in  succession.  By  this  plan  the  observations 
may  be  taken  through  an  aperture  not  much  larger  than  the  loophole  for 
a  musket. 

The  mines  to  be  fired  by  douljlc  observation  are  usually  laid  down  in 
rows  converging  on  the  advance  station  B  (see  Fig.  73),  wliicii  is  there- 
fore generally  set  back  at  some  distance  from  the  river  bank.  This  is 
advantageous,  for  it  gives  more  security  to  the  observing  station  from 
attacking  parties  advancing  by  boats.  The  firing  battery  should  be  at 
A  between  A  and  B.  Station  A  should  be  so  placed  tliat  B  can  be  seen. 
Siiould  the  cable  between  them  become  damaged,  visual  signals  can  then 
be  used,  and  the  battery  "  earthed  "  at  A. 

An  advanced  station  is  sometimes  impracticable.  In  this  case  the 
two  stations  sliould  be  placed  on  opposite  sides  of  the  channel,  and  the 
text-books  (see  Stotlierd's  "  Sulmiarine  Mines  ")  then  recommend  tliat 


Firing  by  Intersection. 


141 


the  mines  should  be  laid  in  rows  across  the  channel,  and  fired  by  separate 
intersections,  a  separate  core  for  each  mine  being  provided  between  tlie 
two  stations,  and  each  electric  circuit  having  two  breaks  in  it,  one  at  A 
and  one  at  B  (see  Fig.  74).  The  plan  requires  a  large  amount  of  mul- 
tiple cable  (as  a  separate  core  for  each  mine  is  required  between  A  and 
B),  and  is  consequently  but  seldom  used  except  for  firing  a  few  advanced 


and  scattered  mines,  which  need  not  be  moored  in  rows.  The  instru- 
ments employed  in  our  service  for  firing  mines  by  horizontal  cross  inter- 
sections, are  termed  "telescopic  observing  and  firing  arcs,"  and  are  fully 
described  with  minute  drawings  on  pages  228    to  231  of   Stotherd's 


"  Notes  on  Submarine  Mining,"  sold  in  New  York.  A  general  idea  of 
the  instruments  may  be  formed  from  the  following  outline  description. 
The  "  firing  ai'c"  employed  at  station  A  consists  of  a  cast-iron  skeleton 
frame  forming  77  deg.  of  a  circle  of  3  ft.  6  in.  radius.  There  is  a  level- 
ling screw  at  each  corner.  The  front  arc  is  so  arranged  that  several 
l2 


148  Submarine  Mining. 

insulated  metallic  foresights  can  be  clamped  to  it.  Each  of  these  is 
situated  in  the  line  of  sight  to  a  distant  mine,  and  each  is  connected  by 
an  insulated  wire  with  the  cable  core  leading  to  that  mine.  A  telescope 
is  mounted  with  its  vertical  axis  to  pivot  on  the  centre  of  the  circle.  A 
light  arm  is  fixed  to  this  axis,  and  sweeps  round  with  the  telescope  and 
just  under  it.  The  arm  carries  a  contact-making  point  at  its  outer  ex- 
tremity, which  is  connected  to  the  tiring  battery  by  an  insulated  wire 
secured  to  the  arm,  and  leaving  it  at  the  inner  end.  The  lead  to  the 
firing  battery  passes  through  a  key  under  the  control  of  the  observer. 
In  case  the  front  sights  should  slip  after  the  mines  are  laid,  the  tele- 
scope is  provided  with  a  horizontal  graduation  and  vernier.  The  tele- 
scope is  set  on  a  distant  fixed  point  and  the  reading  taken,  and  as  each 
mine  is  laid  the  reading  is  taken.  The  correct  positions  of  the  sights 
should  be  tested  daily  by  means  of  the  graduated  arc.  By  these  means 
the  fore  sights  can  be  fixed  afterwards  at  any  time  in  their  correct 
positions.  For  short  ranges  the  telescope  can  be  removed  and  the 
observing  done  through  the  sights.  Suitable  motion  in  azimuth  is 
given  by  a  milled  head  and  gearing.  The  arc  for  the  station  at  B  is 
much  narrower,  because  one  sight  only  is  used.  In  other  respects  it  is 
of  similar  construction,  but  there  is  no  sweep  arm,  the  electric  circuit 
being  closed  by  a  simple  finger  key. 

These  instruments  are  not  intended  to  be  semi-automatic  in  their 
action,  as  might  be  supposed  from  their  construction.  They  are  not  suffi- 
ciently accurate  in  their  mechanical  construction  for  that.  They  are 
used  thus  :  As  soon  as  a  vessel  ai-rives  upon  the  line  of  mines,  as  seen 
fi'om  station  B,  Fig.  73,  the  observer  presses  his  firing  key  during  the 
whole  period  that  any  portion  of  her  hull  is  on  the  line,  thus  "earth- 
ing "  the  firing  battery  at  A. 

The  observer  at  A  moves  his  telescope  until  the  line  of  sight  covers 
the  nearest  mine  to  the  line  of  the  vessel's  advance,  and  if  the  vessel 
come  near  enough  to  this  line  of  sight  he  presses  the  firing  key.  Should 
this  occur  at  the  same  time  that  the  firing  key  at  B  is  pressed,  the  mine 
is  fired.     There  are  several  defects  connected  with  this  system  : 

1.  The  firing  connections  are  exposed  to  the  open  air  and  weather,  as 
the  telescope  cannot  be  worked  accurately  behind  a  glass  screen.  Rain, 
dust,  or  snow  may  consequently  cause  difficulties  at  critical  moments. 

2.  An  electrical  leak  in  the  core  connecting  A  and  B  causes  a  mine 
to  be  fired  when  the  observer  at  A  alone  is  pressing  his  tiring  key. 

3.  Two  instruments  and  two  observers  are  required  for  each  row  of 
mines,  and  as  each  observer  should  have  an  assistant  to  take  his  place 
in  case  of  casualty,  a  large  number  of  trained  observers  are  required. 

■1.   Tlie   construction   of  the    firing  arc   is  not   suited    for    observing 


Firing  hy  Plane  Tahles.  149 

through  a  small  apertui-e,  which  is  now  a(lvisa1)le  on  account  of  the 
development  of  machine-gun  fire. 

Plane  Tables. — Several  systems  depeiul  upon  tlie  plane  table  for 
their  general  application.  The  earliest  forms  were  very  complicated 
and  intricate.  The  one  brought  out  many  years  ago  by  Messrs. 
Siemens  and  Halske,  of  Berlin,  and  since  brought  to  a  high  degree  of 
efficiency,  consists  of  a  plane  table  placed  in  any  secure  position,  and 
carrying  a  chart  to  scale  of  the  mined  waters.  At  the  positions  of  two 
observing  stations  A  and  B  on  the  chart  at  A,  see  Fig.  74,  are  pivotted 
vertically  two  light  aluminium  arms  which  sweep  horizontally  over  the 
chart,  one  slightly  over  the  other,  when  actuated  by  electric  currents 
that  move  a  system  of  electro-magnets  in  connection  with  them. 

The  currents  are  produced  by  the  motions  of  magneto-induction 
apparatus  operated  at  each  of  the  observing  stations  by  the  same  winch 
handle  that  moves  the  telescope  in  azimuth.  It  is  so  arranged  that 
each  telescope  and  the  aluminium  arm  with  which  it  is  connected 
electrically  in  the  chart-room  are  always  parallel  to  one  another  in  their 
projections  on  the  horizontal  plane.  Consequently,  when  the  telescope 
points  on  a  certain  actual  position,  its  aluminium  arm  points  in  the 
same  position  as  indicated  upon  the  chart.  If  the  two  telescopes  are 
pointing  on  the  same  object  the  intersection  of  the  aluminium  arms 
projected  upon  the  chart  indicates  the  position  of  the  object  on  the 
chart.  If  the  mine  positions  are  plotted  on  the  chart  the  observer  in 
the  chart-room  can,  therefore,  at  once  see  whether  a  vessel,  which  the 
two  telescope  observers  are  following,  crosses  the  position  of  a  mine, 
and  if  a  firing  key  for  that  mine  be  at  his  hand  he  can  fire  the  mine  at 
the  correct  moment  of  time.  With  this  system  a  large  number  of 
mines  can  be  operated  by  two  instruments.  But  this  is  a  positive 
disadvantage  when  several  vessels  attempt  to  rush  through  the  mined 
waters  nearly  simultaneously.  Electric  caution  bells  should  be  rung  or 
other  signals  made  in  the  chart-room  by  the  distant  observers,  in  order 
that  the  chart  observer  may  know  when  the  telescopes  are  on  a  vessel ; 
and  the  greatest  care  is  necessary  to  prevent  the  observers  directing 
their  telescopes  on  different  vessels,  or  on  different  parts  of  the  same 
vessel. 

The  instruments  are  very  costly,  and  some  arrangement  which  is  less 
complicated  and  difficult  to  keep  in  order  is  preferable.  The  principal 
merit  of  the  plan  lies  in  the  fact  that  the  firing  arrangements  are 
under  the  control  of  an  operator  in  a  secure  bomb-proof,  and  that  the 
observers  have  simply  to  use  their  telescopes  and  ring  or  not  ring  the 
caution  bells  which  they  control. 

The  following  arrangement,    which   is  much   simpler,   has  just   been 


150 


Submarine  Mining. 


patented  by  the  writer.  The  mines  are  usually  arranged  in  two  rows 
to  converge  on  an  observer  at  B  (see  Fig.  75).  If  four  rows  are  re- 
quired a  second  advanced  observer  at  0  is  required.  The  observer  at  A 
is  situated  over  a  bomb-proof,  and  the  telescope  can  be  fixed  to  a  vertical 
axis  carried  down  into  the  said  chamber.  This  vertical  rod  or  tube 
carries  a  light  horizontal  arm  near  to  its  lower  extremity,  so  that  the 
arm  and  telescope  are  traversed  simultaneously.  The  arm  sweeps  over 
a  plane  table  with  a  scaled  chart  of  the  mined  waters  upon  it.  The 
destructive  area  of  each  mine  is  represented  by  a  small  platinised  metal 
button,  which  is  connected  by  an  insulated  wire  with  the  mine  itself. 
The  arm  carries  a  straight-edge  contact-maker,  a  stretched  wire  forming 
a  convenient  arrangement  for  this  purpose.    The  straight  edge  is  divided 


at  a,  b,  c,  d,  e  by  insulators,  each  situated  at  a  point  intermediate 
between  the  scaled  distance  from  A  of  the  most  distant  mine  in  each  of 
the  inner  lines,  and  the  nearest  mine  in  the  next  outer  line  ;  the  mines 
being  so  planted  that  the  latter  distance  exceeds  the  former.  These 
sections  of  the  firing  arm  are  normally  insulated,  but  are  connected  in 
pairs,  each  pair  to  two  platinised  contact  points.  No.  1  and  No.  2, 
forming  part  of  a  small  instrument  illustrated  on  Fig.  76.  A  tongue  t 
normally  midway  between  these  two  points  is  platinised,  and  is  con- 
nected to  the  firing  battery  F  B.  The  tongue  t  is  carried  on  the  ex- 
tremity of  an  armature  mounted  on  an  insulated  axis  o.  The  armature 
consists  of  a  small  flat  permanent  magnet,  with  a  soft  iron  bar  rivetted 
on  eitliei-  side  of  it.      The  regulating  .springs  11  R  witli  set  screws  S  S 


Neiu  Met] tods  Described. 


lol 


keep  the  armature  in  a  central  position  between  the  horns  of  an  electro- 
magnet M  N  when  no  electric  current  is  passing.  A  small  battery  to 
"  earth"  E  at  station  B  (or  C)  is  connected  to  a  single  core  leading  to  A 
by  two  double  contact-makers,  so  that  a  pull  on  No.  1  cord  (Fig.  77) 
will  actuate  tongue  <  at  A  to  stud  No.  1,  and  a  pull  on  cord  No.  2  will 
move  «  at  A  to  stud  No.  2.  The  observer  at  B  or  C  therefore  simply 
pulls  cord  1  during  the  passage  of  a  vessel  across  line  1,  and  cord  2 
during  her  passage  across  line  2. 


The  observer  at  A  keeps  his  telescope  on  the  vessel,  and  pulls  a 
contact-maker  with  his  foot  or  knee  so  long  as  the  crosshairs  of  his 
telescope  point  fairly  on  the  object.  If  the  vessel  come  within  the 
sphere  of  action  of  a  mine  it  is  consequently  fired  at  the  right  moment. 

The  above  arrangements  are  capable  of  several  modifications.  For 
instance,  two  cores  may  connect  A  and  B,  and  two  electric  bells  of 
difierent  tones  may  be  rung  from  B,  one  when  the  vessel  is  passing  line 
1,  the  other  when  she  is  passing  line  2.  In  this  case  there  siiould  be 
a  chart-room  operator  who  would  prime  that  section  of  the  straight- 
edge which  fires  the  mine  in  the  line  corresponding  to  the  ringing  bell. 
The  observer  at  A  would  simply  follow  the  vessel  with  his  telescope, 
informing  the  chart-room  operator  in  some  manner  (electrically  or 
vocally)  when  he  is  on  or  off  the  object.  Again,  the  electric  communi- 
cation between  A  and  B  may  be  broken,  or  never  made,  and  visual 
signals  from  B  would  then  be  resorted  to. 

Instruments  of  the  kind  to  be  erected  in  a  hurry,  should  have  the 
plane  table  and  chart  placed  immediately  under  the  telescope,  the 
whole  being  set  up  by  three  levelling  screws  on  the  top  of  a  parapet. 
Moreover  it  may  then  be  desired  to  avoid  tlie  use  of  the  auxiliary 
instrument,  see  Fig.  76,  and  perhaps  to  rely  upon  visual  signals 
from  advanced  observers.  Under  such  conditions  the  mines  can  be 
planted  so  that  the  lines  are  directed  upon  any  suitable  points   I.,   II. , 


152 


Submarine  Mining. 


II T.  IV.  (see  Fig.  78),  which  can  be  situated  on  either  side  of  the 
channel.  Thus  a  red  ilag  by  day  or  a  red  light  by  night  displayed  by 
observer  I.,  would  indicate  a  vessel  on  line  I.  Ditto  at  III.  for  that 
line.     A  green  Hag  or  ligiit  at  II.,  and  also  at  IV.     At  night  a  white 


light  at  each  of  these  advanced  posts,  and  screened  towards  the  front, 
would  be  directed  continuously  on  A  to  indicate  their  positions  to  tin' 
central  observer.  If  wires  be  laid  to  I.,  II.,  III.,  IV.,  subsequently,  it 
can  be  done  as  shown  on  Fig.  78. 

I  prefer  to  use  only  two  lines,  as  a  general  rule,  in  connection  with 
one  plane  table,  because  a  sufficient  number  of  mines  can  usually  be 
planted  in  two  lines,  for  one  central  observer  to  attend  to,  and  his 
actions  would  be  hampered  if  he  or  his  assistant  had  to  attend  to 
several  outlying  observing  stations.  When  four  lines  are  used  it  is 
therefore  better  to  employ  two  plane  tables  at  A,  each  having  two  lines 
plotted  upon  it.  When  this  is  done  in  connection  with  dispersed 
observers  to  the  front,  the  further  the  two  lines  on  each  plane  table  are 
separated  the  better,  because  there  is  then  less  liability  to  make  mis- 
takes. Consequently  one  plane  table  should  take  lines  I.  and  III. ;  the 
other,  lines  II.  and  IV.,  and  the  advanced  observers  be  placed  accordingly. 

It  may  sometimes  occur  that  mines  have  to  be  planted  behind  the 
central  station  A,  in  which  case  the  same  arrangements  are  applicable, 
the  outer  observers  being  located  towaids  tlie  rear  of  the  general 
position. 

When  a  channel  is  very  broad,  each  side  may  conveniently  be  dealt 
with  separately,  the  mines  on  each  side  channel  being  planted  in  lines 
converging  in  the  other  station.     Thus,    in    Fig.   70,  tlie  mines  in   the 


New  Methods  Described. 


153 


right  channel   would   be  laid   in   lines  converging  on   station    B,  and 
within  the  ring  areas  described  from  A  as  centre.     Also  the  mines   in 

I 


the  left  channel  would  be  laid  so  as  to  converge  on  A,  and  would  l>e 
connected  to  a  plane  table  in  B.  The  central  portion  of  the  cliannel 
could  conveniently  be  mined  with  electro-contact  arrangements. 

It  will  be  noted  that  in  this  system  of  firing  by  observation,  tlie 
angles  of  intersection  do  not  vary  greatly  from  the  best  possible  angle, 
viz.,  90  deg. 

In  conclusion,  it  sliould  be  observed  that  whatever  arrangement  be 
used  for  firing  by  observation,  it  should  be  simple,  not  liable  to  get  out 
of  order,  well  protected,  effective  when  the  vessel  of  a  foe  is  enshrouded 
in  smoke.  Every  arrangement  possesses  certain  inherent  defects  and 
advantages.  It  is  for  the  adept  to  select  the  one  which  he  considers 
best  adapted  for  any  required  conditions  and  locality. 


154 


CHAPTER  XIT. 
The   Firing    Station. 

The  number  of  wires  unavoidable  in  every  important  firing  station 
necessitates  a  methodical  system  of  connecting  and  placing  same.  This 
is  especially  the  case  in  our  service,  where  the  firing  and  testing  gear  is 
intricate.  An  excellent  system  has  been  elaborated  at  Chatham  under 
the  able  directions  of  Captain  G.  A.  Carr,  R.E.  A  descrijition  is  not 
permitted,  and  if  given  (with  permission)  it  would  simply  bewilder  the 
general  reader.  In  fact,  it  requires  a  long  and  careful  training  to 
understand  the  details  of  an  English  test-room.  Moreover,  the  details 
do  not  apply  to  the  arrangements  hereinbefore  advocated,  but  the 
general  idea  of  method,  to  avoid  confusion,  is  applicable  to  all  systems, 
and  should  be  adopted  equally  for  simple  as  for  more  complex  plans. 

Several  sets  of  the  apparatus,  shown  on  Fig.  70,  page  137,  each  on 
its  own  board,  can  be  fixed  on  a  large  deal  board  secured  to  one  of  the 
walls  of  the  room.  On  either  side  of  them  a  batten  of  kiln-dried  teak 
9  in.  or  10  in.  wide,  and  3  ft.  or  4  ft.  long,  can  be  secured,  and  a  number 
of  brass  terminals  fastened  thereto.  The  cable  ends  from  the  mines,  or 
from  the  observing  stations,  or  from  the  telegraph  stations,  in  fact  all 
electric  wires  connected  with  the  firing  station,  can  be  brought  into  the 
room  at  one  of  the  corners,  preferably  near  the  roof.  Each  core  should 
then  be  identified  and  labelled,  and  be  led  to  one  of  the  terminals,  a 
small  descriptive  ticket  being  gummed  on  the  batten  close  to  the  core. 
The  poles  of  the  batteries,  &c.,  should  be  carried  in  like  manner  to 
terminals  on  this  universal  commutator.  The  various  connections  can 
tlien  be  made  easily  and  expeditiously.  The  lead  from  the  firing  battery 
should  be  kept  at  a  distance  from  the  other  leads,  and  need  not  be  taken 
to  the  commutator.  For  the  arrangement  described  it  is  advisable  to 
carry  the  firing  lead  to  the  ceiling  of  the  room,  and  tliore  connect  it  by 
means  of  branch  wires  to  tlie  pull  contact-makers,  one  for  each  set  of 
fuze  signalling  apparatus. 

The  "  Earths." — The  "  earth  "  used  at  the  firing  station  should  consist 
of  a  length  of  2-in.  steel  wire  mooring  rope  carried  to  low-water  mark  in 
a  deep  trench  and  immersed  in  the  sea  for  a  length  of  three  fathoms, 


the  Firing  Battery. 


155 


For  the  arrangement  described  one  "earth"  can  be  used  for  all  the 
batteries,  but  it  is  desirable  to  liave  a  separate  "  earth"  for  tlie  resistance 
test,  and  the  wire  rope  used  for  this  purpose  should  be  carried  to  the  sea 
in  a  trench  separated  as  far  as  possible  from  the  firing  "  earth."  This, 
moreover,  gives  the  power  to  test  the  joint  resistance  of  these  two 
earths.  The  inner  ends  of  these  ropes  should  be  soldered  to  a  copper 
strip,  the  wires  being  laid  out  in  fan-like  form,  and  carefully  soldered  to 
it.  An  insulated  wire  or  wires  can  then  be  led  from  each  "  earth  "  to 
the  battery  pole  or  other  point  to  be  "earthed." 

Insulated  Wires. — The  connections  in  the  firing  station  should  be 
made  with  a  light  insulated  wire  which  is  flexible,  and  not  likely  to 
break  when  bent.  A  good  core  of  the  kind  is  formed  of  three  No.  26 
copper  wires  stranded  and  insulated  with  gutta-percha  or  india-rubber, 
and  with  a  pi'imed  tape  wound  spirally  upon  it. 

Testing  the  Firing  Battery. — One  of  the  most  important  tests  to  be 
taken  at  the  firing  station,  is  that  of  the  efiiciency  of  the  firing  battery. 
This  subject  was  most  scientifically  investigated  by  Captain  (now  Major- 
General)  E.  W.  Ward,  R.E.,  in  the  paper  already  referred  to,  and  which 
was  published  in  1855  in  vol.  iv.,  R.E.  Professional  Papers.     At  that 

FLq.80. 


, 'h      /'•      ?«       ^0      %,       /  i__/—\ 

P 00  0  00  000 

TO  To  30  lo  To  4  3~~1 

0000000)0 


time  he  invented  the  instrument  since  termed  a  thermo-galvanometer, 
the  fusion  of  short  lengths  of  fine  wire  held  between  metal  clips  being 
effected  by  the  battery  under  examination,  and  a  Wheatstone  rheostat 
inserted  in  the  circuit.  The  rheostat  is  a  somewhat  clumsy  and  unsatis- 
factory instrument,  and  resistances  that  can  be  plugged  in  a  box  in  the 
(now)  ordinary  way  are  preferable.  The  box  should  contain  a  range  of 
about  200  ohms,  and  a  good  instrument  of  the  kind  suitable  for  sea 
mining  purposes  which  Messrs.  Elliott  are  about  to  manufacture  is  as 
follows  :  The  box  contains  resistance  coils  ranging  between  ^jV  ohm 
and  211  ohms  which  can  be  taken  in  steps  of  -^^^  ohm  at  any  point.  A 
;|-in.  clip  for  holding  the  wire  or  wires  and  a  finger  key  are  interposed  in 
the  circuit  between  terminals  B  B.  Two  additional  resistances  of  1 0  or 
12  ohms  each  are  added  for  balancing  by  Wheatstone's  bridge  when 
required  (see  Fig.  80),  and  two  terminals  GG  for  the  galvanoscope  con- 
nections.    For  such  a  test  the  unknown  resistance  is  connected   to  rx. 


156  Submarine  Mining. 

The  resistance  coils  ai-e  made  of  wire  sufficiently  thick  to  give  correct 
results  with  currents  from  the  firing  batteries,  prolonged  contact  at  the 
key  being  avoided.  When  testing  a  firing  battery  the  resistance  first 
unplugged  should  be  less  than  the  estimate,  and  the  wire  is  fused 
before  the  battery  has  time  to  polarize.  An  inspection  of  the  fusion  will 
assist  the  operator  in  his  next  estimate.  After  a  few  trials  the  ex- 
treme limit  of  power  of  the  battery  is  determined  for  fusing  one  wire. 
Similarly  the  limit  of  the  power  of  the  battery  to  fuse  two  wires  in  the 
clip  in  multiple  arc  is  found. 

Then  if  C  denote  the  current  required  to  fuse  one  standard  wire  (the 
wire  employed  usually  represents  that  which  is  employed  in  the  fuzes), 
and  if  R  and  Rl  denote  the  external  resistances  found  in  each  test, 
and  if  L  denote  the  liquid  resistance  of  the  battery  under  trial,  and  if 
E  denote  the  electromotive  force  of  the  battery  ;  we  have 

E  =  C  (R  +  L)  by  first  test  (one  wire), 
and 

E  =  2  C  (R'  +  L)  by  second  test  (two  wires). 

.-.  R  +  L  =  2Ri  +  2Lancl  L  =  R-2Ri. 

The  .ippi'oximate  resistance  of  the  standard  wire  at  fusing  point 
should  be  determined  previously  by  other  processes.  This  should  be 
added  to  the  unplugged  resistance  in  the  first  test  to  give  R  ;  and  one- 
half  of  it  should  be  added  to  the  unplugged  resistance  in  the  second 
test  to  give  R'. 

0  should  also  be  a  known  quantity,  and  as  E  =  C  (R  4-  L)  wc  can 
calculate  the  electromotive  force  of  the  battery  directly  its  liquid 
resistance  L  is  found. 

But  a  special  instrument  for  testing  resistances  by  means  of  currents 
up  to  about  1  ampere  is  not  required  when  the  firing  station  is  provided 
with  one  of  my  resistance  coil  arrangements  illustrated  on  page  137, 
a  clip  for  the  wire  bridge  connection  being  added  to  the  instrument  at 
the  infinity  plug  brasses  and  the  resistances  up  to  the  100  ohms  plug 
being  formed  of  wires  that  do  not  become  heated  by  short  currents  up 
to  1  ampere.  By  these  means  the  same  instrument  can  be  employed 
for  all  purposes. 

The  wire  clip  can  form  part  of  the  instrument  or  be  separated,  as 
desired.  In  the  latter  case  an  extra  terminal  is  required  connected  to 
tlie  brass  of  the  infinity  plug. 

TcMimj  the  other  Batteries.— The  other  batteries  can  be  tested  readily 
by  means  of  a  handy  little  instrument  invented  by  the  late  Mr.  E.  O. 
Browne,  assistant  at  the  Chemical  Department,  Royal  Arsenal,  Wool- 
wich. It  is  a  small  vertical  detector  with  gravity  prepondei'ance  for 
zero  and  having  three  coils  of   1000,  10,   and   l2  ohms  resistance  respec- 


Testinj/  the  otlier  Batteries.  157 

tively,  any  one  of  wliich  can  he  used,  a  plug  commutator  on  tlio  top  of 
the  mahogany  case  being  provided  for  this  purpose.  A  powerful  per- 
manent horseshoe  magnet  is  usually  employed  for  controlling  the  de- 
flections. This  magnet  should  be  placed  with  its  axis  in  line  with  the 
axis  of  the  needle  at  a  certain  defined  distance  behind  the  galvano- 
meter. The  dial  of  the  instrument  should  be  graduated  thus  :  A 
battery  of  twenty  low  resistance  Daniell  cells  should  be  placed  in 
circuit  with  the  1000  ohms  coil,  and  the  deflection  taken  and  marked. 
The  current  is  then  reversed  and  the  deflection  taken  on  the  other  side 
of  the  dial.  The  battery  is  then  reduced  cell  by  cell,  and  the  deflec- 
tions marked  and  numbered  to  accord  with  the  number  of  volts  wliich 
produce  them.  Finally,  readings  are  taken  with  the  2  ohms  coil,  and 
one  cell  in  circuit.  The  mean  reading  is  compared  with  the  mean 
reading  produced  by  the  same  cell  through  the  1000  ohms  coil,  and  this 
comparison  is  usually  called  the  constant  of  the  galvanometer.  It  is 
generally  about  six  in  the  instruments  made  by  Messrs.  P^lliott 
Brothers.  Whatever  it  be,  call  it  M ;  and  if  d  be  the  deflection  on  the 
1000  coil  and  D  that  on  the  2  coil,  then  M  rf=  D. 

This  result  being  obtained  with  a  cell  of  low  internal  resistance  L 
and  a  potential  V,  we  have 

V-^('2  +  L)  ampures  producing  D, 
and 

V4-(1000  +  L)  amperes  producing  (/. 
If  a  resistance  x  be  now  inserted  in  circuit,  we  have  a  current 

V  -^  (2  +  L  +  a;)  producing  a  deflection  I)', 
and  a  current 

V-e-(1000  +  L  +  a)  producing  a  deflection  dK 
If  X  be  small  as  compared  with  1000 

(/  =  (/'  andD=M(?i. 
And  as 

Dor  M</i:D'  ::2  +  L  +  a;:2  +  L 

"'■""("":') 

If,  therefore,  we  know  the  original  liquid  resistance  L  of  a  low- 
resistance  cell  producing  M  d=T>,  we  can,  by  means  of  the  above 
formula,  discover  any  alteration  in  resistance  producing  some  inequality 
between  M  d^  and  D'.  Moreover,  the  formula  applies  equally  whether 
X  be  an  internal  or  an  external  resistance  to  the  battery  cell,  or  whether 
it  be  added  or  sul)tracted,  its  relative  value  being  small  as  compared 
with  1000.  The  formula  is  not  absolutely  accurate,  as  the  foregoing 
indicates,  but  it  is  sufficiently  accurate  for  all  practical  purposes  when 
the  resistances  to  be  measured  are  low,  and  it  is  especially  useful  for 
finding  approximately  the  internal  resistances  of  small  voltaic  batteries. 


158  Suhmarioie  Mining. 

Their  relative  potentials  are  also  found  approximately  by  comparing 
d  and  c?\  the  deflections  on  the  1000  ohms  coil.  If  a  fall  of  one-tenth 
of  the  potential  occur  in  a  battery,  it  should  be  seen  to.  The  various 
batteries  set  up  for  a  system  of  mines  should  be  tested  daily,  for  resist- 
ance and  potential ;  and  the  results  recorded  in  tabular  form  on  a  book 
kept  for  the  purpose. 
,'  Testing  a  Shutter  Apjmratus. — AVhen  a  shutter  signalling  apparatus 
is  employed  (see  Fig.  69,  page  134),  it  is  desirable  to  test  same  daily  by 
dropping  the  shutter  (taking  care  that  the  firing  battery  is  not  plugged) 
and  then  plugging  a  clip  and  one  or  two  low-resistance  cells  to  the  ends 
of  wires  W  W  to  note  whether  the  fine  wire  is  reddened.  (The  small 
battery  and  ring  bell  should  be  plugged  out  of  circuit.)  This  tests  the 
efficiency  of  the  spring  contacts.  The  results  should  be  recorded  in  the 
book. 

The  Shutter  Adjustment. — The  adjustment  of  the  tension  of  the 
armature's  controlling  spring  c  (Fig.  69)  cjepends  upon  the  electrical 
sensitivity  of  the  shutter  apparatus,  and  this  depends  not  only  upon  the 
number  of  convolutions  in  the  coils  and  the  distance  of  the  poles  from 
the  armature,  but  also  and  to  a  great  extent  upon  the  mechanical 
arrangements  of  the  shutter  itself.  In  the  apparatus  shown  on  Fig.  69 
the  lever  is  arranged  so  that  the  longest  portion  is  towards  the  armature, 
a  high  mechanical  sensitivity  being  thereby  obtained.  The  preponder- 
ance of  the  index  end  should  be  kept  low,  the  contact  friction  which 
impedes  the  movement  of  the  armature  is  thereby  minimised.  The 
contact  points  must  be  kept  bright  and  scrupulously  clean,  this  being 
seen  to  daily,  and  oftener  if  a  stove  or  a  smoky  fire  is  in  the  room.  For 
this  reason  it  is  desirable  to  keep  the  room  dry  by  hot  water  or  hot-air 
pipes  which  produce  no  dirt  and  dust.  When  each  mine  contains  a 
testing  apparatus,  a  current  from  the  signalling  battery  is  constantly 
passing  through  each  shutter  coil,  and  the  strength  of  signal  (;'.e.,  the 
current  that  causes  the  shutter  to  fall)  is  consequently  the  difierence 
between  the  normal  current  and  that  produced  temporarily  by  the 
circuit-closing  arrangement  in  the  mine  when  it  is  subjected  to 
mechanical  shock.  In  the  arrangements  proposed  in  a  previous  chapter 
herein  this  matter  is  simplified,  because  the  branch  cables  to  the  mines 
are  all  insulated  until  a  circuit-closer  is  actuated.  The  strength  of 
signal  is  then  the  whole  current  produced  by  the  signalling  battery 
passing  through  the  external  resistances  in  circuit,  viz.,  earth  at  home, 
cable  core,  electro-magnet  coils  at  circuit-closer,  fuzes,  and  earth  abroad. 
This  current  will  vary  according  to  the  distance  of  the  mines  from  the 
firing  station,  and  tlie  consequent  variations  in  the  line  resistance. 
AVlicii  a  line  becomes  leaky,  due  to  faulty  insulation,  there  will  be  a  con- 


Test'mg  the  Instruiucnfs.  1.VJ 

tinuous  current  tlirough  tlie  leak  from  the  signalling  batteiy.  In  sucii 
case  the  strength  of  signal  is  equal  to  the  difference  betwc(;n  this  current 
and  that  produced  when  the  mine  circuit-closer  acts. 

It  is  necessary  to  provide  a  separate  signalling  battery  for  a  leaky 
line,  separating  the  group  from  the  remainder  of  the  system  served  by 
the  same  shutter  apparatus  of  seven  indices,  but  the  leak  should  be 
seen  to  at  once  and  repaired,  and  this  complication  removed  as  soon  as 
possible.  "With  good  gear  and  good  care  leaks  seldom  should  occur, 
and  the  moment  the  resistance  tests  show  the  commencement  of  a  leak 
the  mine  field  working  parties  should  attack  it,  for  it  is  almost  certain 
to  develop  rapidly,  and  perhaps  make  the  whole  of  a  group  useless.  It 
is  generally  produced  by  the  chafing  of  a  cable  near  to  or  at  a  cable 
grip,  especially  when  the  mines  are  subject  to  the  swaying  motions 
caused  by  strong  currents  of  water. 

Having  discovered  by  experiment  the  minimum  mechanical  sensitivity 
at  which  a  shutter  should  be  adjusted,  it  is  easy  to  discover  what  current 
through  the  coils  will  just  release  it,  and  as  the  shutter  coils  are  similar 
to  each  other,  this  same  adjusting  current  can  be  used  for  all  of  them. 

Each  coil  should  be  tested  daily  in  this  manner,  and  the  shutter  sen- 
sitivity altered  if  necessary  by  means  of  the  regulating  spring  c  (Fig.  69), 
until  it  accords  with  the  adjusting  current.  It  is  well  to  commence  each 
test  by  trying  a  rather  smaller  current,  gradually  increasing  same  until 
the  shutter  falls.  The  current  durations  given  by  a  key  should  be  short, 
or  residual  magnetism  in  the  soft  iron  cores  of  the  electro-magnet  will 
cause  difliculties. 

All  this  is  rather  harassing,  and  the  shutter  battery  is  found  to  give 
a  lot  of  trouble.  The  employment  of  a  system  in  which  no  shutter 
apparatus  is  required,  as  already  explained  on  page  136,  is  therefore  an 
important  improvement. 

Testing  the  Instruments.— The  electrical  instruments  employed  in  a 
firing  station  should  occasionally  be  tested.  The  resistance  coils  should 
be  balanced  against  one  another.  The  plugging  brasses  should  be 
frequently  cleaned.  Each  galvanometer  or  galvanoscope  should  be  tried 
with  a  given  current  to  see  that  its  sensitivity  remains  unimpaired. 

Testing  for  Insulation. — -After  the  mines  are  laid,  it  is  seldom,  if 
ever,  necessary  to  test  a  line  for  insulation,  the  resistance  test,  as 
recorded  by  a  set  of  resistance  coils,  being  a  sufiicient  test  for  sea 
mining  efficiency.  As  has  been  stated,  however,  some  of  the  main  cables 
may  with  advantage  be  laid  permanently  in  situ,  their  far  ends  being 
insulated.  These  should  be  tested  for  insulation  periodically — say  every 
quarter.  Moreover,  the  other  cables  stored  in  tanks  at  the  store  depot 
should  be  tested  similarly. 


160  Submarine  Mining. 

In  our  service  elaborate  tests  are  the  fashion,  a  condenser  i^  micro- 
farad, and  a  i-eflecting  galvanometer,  forming  part  of  the  equipment  of 
each  important  submarine  mining  depot. 

No  useful  purpose  is  served  by  obtaining  the  exact  insulation  resist- 
ance per  knot  of  each  piece  of  cable  stored  in  the  cable  tanks.  A 
much  rougher  test  for  insulation  is  sufficient,  and  direct  testing  by 
Wheatstone's  bridge  being  thoroughly  understood  by  many  of  the  men, 
it  is  better  to  employ  it  for  these  tests.  This  can  be  done  if  each 
depot  is  supplied  with  a  graphite  resistance  of  1  megohm,  and  two  sets 
of  resistance  coils,  each  of  10,000  ohms.  A  sensitive  astatic  is  then  all 
that  is  required,  and  it  is  very  useful  for  a  number  of  other  purposes. 
This  galvanometer  should  be  portable,  and  easily  set  up  anywhere  on 
a  steady  and  level  platform. 

Sensitive  Astatic  Gahamnneter. — An  excellent  instrument  was  made 
by  Messrs.  Elliott  Brothers  in  1880  from  a  design  and  directions  given 
by  the  author.  It  has  been  used  for  many  purposes  since,  and  is  an 
exceedingly  useful  and  trustworthy  instrument.  It  has  a  fibre  suspen- 
sion of  fine  silk,  and  the  needle  is  supported  by  a  mechanical  contrivance 
when  the  instrument  is  not  in  use.  It  can  then  receive  rough  usage 
without  fear  of  damage.  Astatic  galvanometers  made  with  an  agate 
and  point  suspension  are  constantly  getting  out  of  order,  the  inertia  of 
the  needle  breaking  or  cracking  the  agate  plate  when  the  instrument 
receives  a  shock. 

Not  unfrequently  these  galvanometers,  altliough  carefully  packed,  are 
damaged  in  transit  and  arrive  at  stations  on  the  other  side  of  the  world 
in  a  useless  condition,  and  are  not  easily  repaired  locally.  The  fibre 
suspension  galvanometer  is  free  from  this  defect.  It  is  mounted  on  a 
square  ebonite  block.  Its  resistance  is  about  4000  ohms.  It  has  a 
sensitivity  of  12  megohms  per  volt  (that  is  to  say,  1  volt  produces 
1  unit  of  deflection  through  a  resistance  of  12  megohms),  when  no  con- 
trolling magnet  is  used  to  bring  the  needle  quickly  back  to  zero,  and 
with  the  controlling  magnet  it  can  easily  be  adjusted  to  give  8  megohms 
per  volt.  (The  maximum  sensitivity  of  the  astatic  used  for  submarine 
mining  in  our  service  is  only  |  megohm  per  volt.) 

The  instrument  is  provided  with  a  brass  cylindrical  cover  ;uid  glass 
top.  This  can  be  removed,  if  desired,  when  testing,  and  small  wooden 
stops  placed  on  either  side  of  the  needle  so  as  to  prevent  undue  motion 
and  loss  of  time  thereby.  The  whole  is  contained  in  a  small  l)ox  about 
6  in.  cube. 

21i,e  Megohm  liesistance. — Many  years  ago  Mr.  Johnson,  of  the  well- 
known  firm  of  Johnson  and  Phillips,  electrical  engineers,  published  a 
description    in    the    Philosophical    Magazine    of  a    grapliite    resistance 


Testing  for  InsiUatlon. 


161 


formed  by  a  peiu-il  mark  on  a  l)lock  of  vulcaiiitc,  and  on  Scptemlx>r  2, 
1879,  he  wrote  me  a  letter  on  the  subject,  wherefroni  the  following 
extracts  are  taken  : 

"  My  first  idea  was  to  make  them  on  vulcanite,  because  of  the  com- 
parative ease  with  which  the  i-esistance  was  adjusted  to  the  required 
\'alue.  After  a  line  had  been  made  with  a  moderately  hard  pencil,  and 
when  the  shellac  varnish  with  which  it  was  covered  had  become  hard, 
it  was  easy  with  the  point  of  a  sharp  knife  to  scrape  away  the  plumbago 
so  as  to  reduce  the  width  of  the  line  until  the  required  resistance  was 
obtained,  but  my  experience  has  been  that  those  made  on  vulcanite  do 
not  stand  well,  and  I  have  attributed  this  to  the  sulphur  working  to  the 
surface,  as  we  know  it  does,  and  so  destroying  the  continuity.  But  with 
glass,  although  we  have  a  good  permanent  resistance,  the  power  of  ad- 
justment by  scraping  away  the  width  of  the  line  is  lost.  The  resistance 
has,  therefore,  to  remain  whatever  it  may  turn  out  to  be  when  first 

made." "  One  point  I  have  noticed  which  is  very  curious 

.  .  .  .  viz.,  that  as  the  battery  power  is  increased  the  resistance 
falls  slightly,  that  is  to  say,  with  500  cells  the  resistance  would  be 
perhaps  between  1  and  2  per  cent,  lower  than  with  200  cells,  but  when 
the  ratio  of  this  increase  has  been  carefully  measured,  it  is  easily 
allowed  for.  I  have  tested  several  with  1000  cells,  and  immediately 
afterwards  with  100,  and  found  the  resistance  had  not  altered,  although 

with   the  higher  power  it  gave  a  slightly  lower  value 

A  good  deal  of  care  is  necessary  in  making  them,  and  one  generally 
has  several  failures,  but  by  practice  I  find  that  it  is  possible  to  get 
pretty  nearly  the  resistance  required.  For  instance,  I  recently  made  a 
megohm  ;  when  finished  it  came  out  1.08  megohm." 

The  method  of  taking  the  insulation  test  of  a  cable  with  the  above 
instruments  is  depicted  in  Fig.  81,  where  0  is  the  cable  in  the  sea  or 
Rg.8l 


100  cells 

tank  T,  having  the  end  I  insulated  and  the  other  end  connected  through 
a  Post  Office  pattern  set  of  resistance  coils  R  to  the  testing  battery  by 
the   key   K.   Also,  the  meohm  resistance  is  similarly  connected  through 

M 


162  Siihviarine  Mining. 

W  to  K  and  tlie  testing  battery.  The  galvanometer  G  is  then  con- 
nected across  the  bridge  by  the  K'  as  sliown,  and  the  test  can  be  taken 
in  the  usual  way,  key  K  being  used  for  the  battery,  and  key  K'  for  the 
galvanometer. 

The  resistance  R'  is  made  10,000,  and  R  is  adjusted  until  G  gives  no 
dellection.  Then  the  insulation  resistance  x  of  the  cable  is  found  by 
the  proportion 

R:x::B}:Q:i  10,000  :  1,000,000  :  :  1  :  100 

or 

a-:=Rfi^Ri=100R. 

TestliKj  the  Observing  Instruments,  &c. — When  time  permits  the  elec- 
trical parts  of  the  observing  instruments,  call  bells,  Ac,  should  be  tested 
for  continuity  and  insulation,  all  contact  points,  plug  holes,  and  plugs, 
&,c.,  being  kept  bright  and  clean.  Also  the  leading  wires  should  be  ex- 
amined frequently,  and  every  care  taken  to  keep  the  whole  in  thorough 
working  order. 


In  a  paper  on  "  The  Electrical  Resistance  of  Conductors  at  High 
Temperatures,"  contributed  to  the  R.E.  Institute,  1878,  by  the  author, 
the  following  conclusion  was  arrived  at,  and  the  results  mentioned  by  Mr. 
Johnson  (see  last  page)  are  probably  due  to  a  similar  cause,  viz.,  a 

molecular  torsion  produced  by  the  electricity "  The  results  .... 

appear  to  substantiate  the  idea  which  previous  experiments  suggested 
to  me,  viz.,  that  a  conductor  heated  by  a  current  of  electricity  oti'ers  a 
smaller  resistance  than  when  heated  by  other  and  external  means  to 
the  same  temperature."  .... 

"  It  appears  probable  that  the  action  may  be  analogous  to  that  which 
ol)tains  in  an  insulating  medium  when  an  increase  in  the  electromotive 
force  applied  produces  a  decrease  in  the  resistance  of  the  di-electric." 


163 


CHAPTER  XIII. 
The  Store  Depot. 

The  efficiency  of  many  of  the  arrangements  connected  witli  sea 
mining  centres  upon  good  work  and  good  methods  at  the  central  store 
depot.  Numerous  considerations,  principally  connected  with  the  water 
traffic,  prevent  mines  being  laid  permanently,  so  that  it  is  of  the  utmost 
importance  to  arrange  so  that  they  can  be  laid  quickly  and  properly 
when  the  order  is  given  to  do  so.  The  various  stores  sliould  therefore 
be  prepared  and  labelled.  In  labelling,  the  best  plan  is  to  use  numbers, 
and  to  keep  a  record  book  showing  the  mine  and  group  to  which  any 
number  refers. 

The  Wire  Rope  should  lie  cut  to  the  proper  lengths  and  each  end 
prepared  with  an  eye  and  thimble,  or  whatever  the  system  adopted  may 
be  ;  a  shackle  should  also  be  connected  to  each  eye.  These  mooring 
lines  should  then  be  oiled,  number  labelled,  and  put  away  in  batches, 
those  for  each  group  of  mines  being  tied  together  in  one  batch. 

The  Tripping  Chains  (galvanised)  should  be  prepared  in  a  similar 
manner,  an  iron  ring  added  at  one  end,  and  a  shackle  attached.  The 
chains  for  one  group  sliould  lie  in  one  heap. 

The  Junction  and  Connecting  Boxes,  the  Multiple  Connectors  and 
Disco7inectors,  and  all  gear  of  the  kind,  should  be  number  labelled  and 
arranged  systematically. 

The  Mines,  after  being  carefully  tested,  should  be  loaded  and  stored 
in  a  sentry-guarded  bomb-proof,  with  an  overhead  traveller  on  the  roof 
and  a  tramway  on  the  floor.  Should  it  be  inconvenient  to  keep  all  the 
mines  loaded,  a  proportion  only  should  be  loaded,  viz.,  those  to  be  laid 
first.     The  mines  should  be  number  labelled. 

The  Apparatus  for  each  mine  should  be  carefully  adjusted,  number 
labelled,  and  put  away  in  a  dry  place.  The  apparatus  should  not  be 
loaded  with  the  priming  charge  and  detonating  fuzes  until  the  order  to 
lay  the  mines  has  been  given. 

The  Primary  Charges  of  dry  explosive  may,  therefore,  be  stored  in 
hermetically  sealed  metal  cases  in  a  store  by  thejnselves. 

The  Fuzes  should  be  stored  in  a  dry  place  at  a  distance  from  any 
explosives. 

m2 


164i  Siibvvirine  Minivg. 

The  Sinkers  may  be  collected  in  tiers  round  a  crane  close  to  some 
portion  of  tlic  tramway,  and  not  far  from  the  pier. 

The  Voltaic  Battery  Cells  should  be  number  labelled  and  stored  in 
boxes  ready  to  be  moved  to  the  firing  stations  at  a  moment's  notice. 
The  salts  for  same  should  be  stored  separately. 

The  Electrical  Instruments  should  be  number  labelled,  be  stored  in 
a  warm  dry  room  in  glass-fronted  cases,  and  be  tested  for  efficiency 
periodically,  records  being  kept  of  same.  Some  of  the  less  delicate 
instruments  can  with  advantage  be  kept  ready  fixed  on  the  walls  or 
tables  of  the  firing  stations  away  from  the  depot. 

The  Buoys  to  be  used  in  connection  with  certain  defined  groups  of 
mines  should  be  stored  suitably  and  be  number  labelled.  Tiieir  moor- 
ing lines  may  be  attached  to  them. 

The  General  Stores,  viz.,  ropes,  flags,  lamps,  Ac,  can  be  kept  in  a 
large  shed  suitably  fitted  and  partitioned  for  the  purpose. 

The  Consumable  Stores,  viz.,  the  tar,  oil,  tallow,  ic,  should  be  placed 
in  another  shed. 

The  Exj)losives  for  the  unloaded  and  spare  or  reserve  mines  should 
be  stored  at  a  safe  distance  from  all.  An  old  hulk  moored  in  an  unfre- 
quented creek  near  at  hand  often  affords  a  convenient  store  of  this 
natui-e.  Wherever  situated,  such  a  store  should  be  carefully  guarded 
at  all  times,  and  the  explosives  be  subject  to  periodical  examination, 
records  being  kept  of  same. 

Tlte  Boat  and  Steamer  Stores,  when  not  on  board,  should  Ije  kept 
separately  from  the  other  stores  to  avoid  confusion. 

The  Boats  should  be  housed  in  suitable  sheds  to  protect  them  from 
the  weather,  a  boat  slip  being  provided  in  connection  therewith. 

The  Electric  Cables  should  be  cut  to  the  required  lengths,  their  ends 
crowned  and  number  labelled,  and  a  piece  of  each  core  about  one  yard 
long  left  at  each  end  for  testing  purposes.  These  ends  should  be 
carefully  insulated  before  the  cables  are  placed  in  the  storage  tanks. 
The  cable  lengths  should  be  stored  so  that  those  first  required  are  on  the 
to]).  Tests  for  insulation  and  conductivity  should  be  taken  periodically 
and  recoi'ds  kept.  The  tanks  may  conveniently  be  placed  near  the 
pier,  and  if  there  be  a  good  rise  and  fall  of  tide  it  is  advisable  to  place 
the  tanks  just  inside  the  sea  wall  at  such  a  level  that  they  will  fill  or 
empty  at  high  or  low  tide  when  a  cock  is  opened  in  a  4-in.  pipe  com- 
municating between  the  bottom  of  each  of  tiie  tanks  and  the  sea  out- 
side. Tliis  saves  labour  in  pumping.  The  tanks  may  be  made  of  iron 
or  concrete.  I  prefer  iron,  as  the  concrete  tanks  are  apt  to  crack  and 
leak,  and  then  give  a  lot  of  trouble. 

A  15-ft.  tank  5  ft.   hi-di  will  hold  about  20  knots  of  single  cable,  or 


Sf,orln(/  Eledviv.  Cahles 


l(i 


about  10  knots  of  multiple,  a  core  of  3  ft.  diameter  being  left  for 
the  single,  and  of  4  ft.  diameter  for  tlic  multiple  cable.  The  dimen- 
sions of  tanks  to  contain  smaller  ([uantitifs  may  be  calculated  by  allow- 
ing 40  cubic  feet  of  contents  for  single  cable  and  SO  cubic  feet  for  mul- 
tiple cable,  in  addition  to  the  contents  required  for  the  central  cores. 

The  operations  connected  with  the  cable  laying  are  laborious.  The 
cables  have  to  be  coiled  out  of  the  tank  or  tanks  and  wound  upon 
drums,  which  are  then  transferred  to  the  mooring  steamers,  and  tlien 
taken  to  the  mine  field  and  laid. 

Messrs.  Day,  Summers,  and  Co.,  of  Southampton,  now  undertake  tiie 
manufacture  of  a  barge  designed  and  patented  conjointly  with  the 
author,  and  in  which  iron  cable  tanks  surrounded  by  water-tight  com- 
partments, which  can  be  filled  or  emptied  as  required  for  trimming  the 
barge,  form  part  of  the  structure.  Each  cable  tank  and  ballast  tank 
can  be  filled  from  the  sea  by  a  4-in.  cock,  and  the  level  of  the  water  in 
the  cable  tank  can  be  adjusted  as  desired  by  means  of  a  pump,  and  by 
altering  the  buoyancy  of  the  barge  by  the  ballast  tanks.  A  small  scale 
drawing  of  one  of  these  barges  to  hold  25  knots  of  multiple  or  50  knots 
of  single  cable,  is  given  on  Figs.  82,  83.     When  the  cables  are  stored  in 


aofcji 


this  manner,  those  which  are  required  for  connecting  up  during  the  day's 
work,  are  removed  as  usual  in  the  morning  or  on  the  previous  evening, 
and  the  barge  can  then  be  towed  by  any  tug,  and  the  larger  or  longer 
cables  laid  out  directly  from  the  coils  in  the  barge  tanks.  In  this  way 
many  operations  are  avoided,  and  the  steamers  especially  fitted  for 
mooring  mines  can  Ije  used  for  that  purpose  only.  The  cable  barge  is 
not  well  adapted  for  small  stations,  but  is  useful  and  economical  in  time 
and  labour  at  large  and  important  stations  where  a  number  of  mines 
and  cables  have  to  be  laid  as  quickly  as  possible. 


166 


Submarine  Mining. 


The  Pier. — Each  deput  must  be  provided  with  a  wharf  or  pier  fitted 
with  suitable  cranes,  alongside  Avhich  th('  mooring  steamers  can  lie  at  all 
times  of  tide. 

A  Tramway,  1  ft.  6  in.  gauge,  with  small  iron  trucks  strong  enough 
to  carry  a  load  of  5  or  6  tons,  should  connect  the  various  parts  of  the 
store  depot  with  each  other  and  the  pier-head. 

It  is  not  necessary  to  build  workshops  for  artificers  except  at  those 
stations  where  experiments  or  exercise  are  carried  out  upon  an  extended 
scale  and  for  long  periods,  but  a  portable  forge,  a  carpenter's  bench, 
and  sets  of  tools  for  white  and  blacksmith,  carpenter,  fitter,  and  painter 
should  form  part  of  the  equipment  at  every  depot. 

The  General  Workshop. — One  long  shed  can  advantageously  be  ap- 
propriated as  a  general  workshop  in  which  most  of  the  operations  re- 
quiring cover  from  the  weather  can  be  carried  out.  Small  portions  can 
be  partitioned  off ;  one  for  a  storekeeper's  office,  another  for  electrical 
testing,  a  third  for  fitting  the  apparatus,  and  so  on.  The  size  of  this, 
and  of  all  the  other  sheds,  must  depend  upon  the  number  of  mines,  the 
strength  of  the  working  parties,   &c.     A  diagram  is  given  on  Fig.  84, 


showing  the  general  plan  of  a  depot  for  sea  mining,  but  the  sites,  the 
stf)i-cs,  and  the  conditions  being  so  dillerent  at  various  statioiis  it  must 
be  treated  as  suggestive  and  nothing  more. 

(1)  is  a  l^-ton  whip  hand  crane,  with  a  sweep  of  al)o\it  l.')ft.,  placed  atone 

corner  of  the  pier-head. 

(2)  is  a  5-ton  hand  crane,  with  same  swccj),  jilaced  at  the  other  corner  of  tlie 

pier-head. 

(3)  (.'?)  are  small  turntaliles  for  the  trucks  on 

(4)  (4)  the  18-in.  tramway. 

(5)  (5)  is  the  pier  witli  steps  at  the  inner  angle. 

(0)  is  a  1-ton  crane  or  derrick  for  lifting  the  sinkers  on  the  trucks. 
(7)  (7)  are  the  eahle  tanks. 


The  store  Depot.  1G7 

(8)  (8)  the  boathouse  and  slipway. 

(9)  (9)  the  parade,  available  for  any  open-air  work. 

(10)  general  stores. 

(11)  consumaide  stores. 

(1'2)  l)oat  and  steamer  stores. 

(13)  clerk's  office. 

(14)  superintendent's  office. 

(15)  storekeeper's  office. 

(16)  dry  store  for  instruments  and  other  articles. 

(17)  electrical  test  room. 
(IS)  electrical  fitting  room. 

(19)  general  workshop  provided  with  bays  and  benches. 

(20)  store  for  empty  cases,  buoys,  &c.,  and  provided  with  a  bay  for  hydraulic 

testing. 

(21)  (22)  shifting  and  loading  rooms. 

(2.3)  bomb-proof  magazine  and  store  for  loaded  cases  ;  the  tramway  runs  down 
an  incline  into  the  latter. 

The  Depot  should  be  placed  in  a  secure  position,  and  yet  not  too  re- 
mote from  the  mine  fields,  say  not  more  than  three  or  four  knots  from 
the  fui'thest  mine,  and  as  much  nearer  as  possible.  A  small  creek  run- 
ning back  from  the  main  harbour  may  often  be  found,  and  a  site  selected 
so  that  high  ground  both  hides  and  protects  it. 

At  an  important  station  the  pier-head  must  be  considerably  larger 
than  the  one  shown  on  Fig.  84,  and  a  third  crane  should  be  added  so 
that  two  steamers  can  lie  at  the  pier-head  and  be  loaded  simultaneously  ; 
but  it  is  often  preferable  to  have  two  moderately  sized  depots  rather 
than  one  large  depot,  especially  when  the  mine  fields  are  scattered  and 
separated  by  considerable  distances. 


168 


CHAPTER  XIV. 
Designs  for  Mine  Defence. 

The  fundamental  principles  of  defence  involved  in  tlie  employment 
of  sea  mines  must  now  be  considered,  and  this  will  lead  us  to  the  most 
interesting  work  connected  with  the  subject — viz.,  the  designs  or  chart 
plans  for  submarine  mining. 

They  are  more  intimately  connected  with  fortification  than  most 
people  suppose.  The  positions  of  the  forts  and  batteries,  of  the  mines 
and  cables,  of  the  electric  lights,  of  the  firing  and  observing  stations, 
of  the  telegraphic  and  visual  signalling  forts,  itc,  should  form  one 
harmonious  whole. 

As  no  two  harbours  are  alike,  so  no  two  arrangements  of  fortification 
or  of  mine  defence  will  be  the  same ;  but  the  same  principles  apply  to 
all,  and  they  do  not  differ  greatly  from  the  broad  ideas  that  should 
underlie  the  preparation  of  every  defensive  position.  But  mining 
differs  from  fortification  in  one  important  particular.  The  value  of 
sea  mining  is  greatly  enhanced  when  the  positions,  or  even  the  approxi- 
mate positions,  of  the  mines  are  unknown  to  a  foe.  Secrecy  is  there- 
fore essential.  Not  concealment  as  to  tlie  efticiency  of  the  apparatus 
employed,  or  the  manner  of  its  employment;  but  secrecy  as  to  the 
waters  that  are  mined.  Any  artifice  whicli  ingenuity  can  suggest  should 
be  undertaken,  in  order  to  deceive  a  foe  on  this  score.  Buoys  should 
be  laid,  which  are  otherwise  useless ;  bogus  mining  operations  should 
ostentatiously  be  conducted  for  the  benefit  of  spies  when  time  and 
opportunity  are  available  ;  false  reports  concerning  the  mine  fields 
should  be  spread ;  and  some  of  the  mines,  especially  those  in  advanced 
positions,  may  advantageously  be  laid  at  night  if  possible.  When 
drawing  up  a  design,  the  object  of  a  foe,  and  the  probable  manner  in 
whicli  an  attempt  would  be  made  to  attain  it,  should  be  carefully  con- 
sidered. It  may  be  the  destruction  of  a  dockyard  or  of  a  fleet  at  an 
ancliorage.  It  may  be  tlie  reduction  of  a  sea  fortress,  or  the  capture  of 
a  commercial  city  or  of  a  coaling  station.  The  attack  may  consist  in 
a  bombardment,  or  in  forcing  a  cliannel  at  speed,  or  in  ascending  a 
river  (lclil>eratoly  by  "force  majeure,"  including  perhaps  land  foivos,  as 


Defence  of  Dochyardt^.  1 00 

in  the  American  "War  of  Secession — and  tlie  defence  in  each  case  must 
be  planned  accordingly. 

Let  us  commence  with  the  dockyards.  Mr.  J.  Fergusson  very  truly 
said  in  a  pamphlet  published  a  great  many  years  ago,  and  entitled 
"French  Fleets  and  English  Forts,"  "Turn  and  twist  the  question  as 
we  may,  there  is  no  denying  tlie  fact  that  the  proximate  and  ultimate 
defence  of  England  must  mainly  depend  on  the  fleet,"  .  .  .  the  power 
of  which  "is  wholly  and  absolutely  based  on  the  possession  of  our 
arsenals." 

A  fortified  dockyard  is  not  likely  to  be  attacked  by  land  liy  regular 
siege  made  for  capture,  unless  as  part  of  an  invasion  on  a  large  scale  ; 
but  a  bombardment  from  land  batteries,  or  from  vessels  up  to  perhaps 
12,000  yards  range,  should  be  guarded  against.  However,  neither 
ships  nor  land  batteries  can  effectively  bombard  an  unseen  object  even 
at  much  shorter  ranges  than  12,000  yards.  Consequently,  when  hills 
screen  a  dockyard  from  view,  no  position  beyond  them  need  be  occupied. 
On  the  other  hand,  when  ground  exists  within  bombarding  range  and 
in  sight  of  the  dockyard,  measures  should  be  taken  to  deny  it  to  a  foe. 

It  may  be  asked, — What  has  this  to  do  with  submarine  mining?  Let 
us  take  an  example,  and  see.  Assume  that  a  dockyard  is  dominated 
by  an  island  within  bombarding  distance,  and  that  a  bay  with  a  good 
beach  forming  a  fair  landing  exists  on  the  outer  side  of  the  island. 

Evidently,  the  bay  should  not  only  be  fortified  but  mined.  A  few 
groups  scattered  about  irregularly  between  the  headlands  would  be 
sufficient,  inasmuch  as  their  presence  would  greatly  delay  a  landing 
and  impede  the  work  afterwards  until  they  were  destroyed  or  removed. 
General  Lefi'oy  once  said  that  "When  a  fleet  bombards,  the  opinion  of 
naval  authorities  seems  to  be  that  the  attacking  vessels  should  anchor ; 
if  not,  and  they  continue  in  motion,  their  distance  from  the  object  is 
constantly  varying,  much  of  their  fire  is  thrown  away,  and  they  incur 
numerous  nautical  dangers,"  which  now  certainly  include  sea  mines. 
But  the  operation  of  bombardment  is  a  long  one,  lasting  for  many 
hours,  during  which  the  ships  engaged  in  it  would,  if  anchored,  be 
more  exposed  both  to  the  artillery  and  the  torpedoes  (locomotive)  of 
the  defence,  than  if  the  ships  were  kept  in  motion. 

Guns  cannot  be  considered  efficient  against  ironclads  except  at  ranges 
of  3000  yards  and  under.  The  forts  should  therefore  be  placed  some 
8000  or  9000  yards  in  front  of  the  object  to  be  protected  from  bom- 
bardment. If  this  can  be  done  bombardment  is  practically  prevented, 
for  the  most  powerful  vessels  would  be  much  injured  by  modern  rifled 
guns  at  battering  ranges,  and  such  injuries  would  necessitate  protracted 
repairs  after  any  conflict  with  forts,  and  it  is  highly  improbable  that  a 


170  Submarine  Mining. 

naval  power  would  risk  this  loss  of  efficiency  in  a  fleet  at  a  critical 
time  even  for  a  short  period,  in  order  to  bombard  a  dockyard  at  long 
range.  Sometimes,  however,  it  is  impossible  to  place  forts  so  far  to  the 
fi'ont,  and  in  such  a  case  a  zone  of  water  will  exist  from  which  a  fleet 
may  bombard  and  yet  be  outside  the  effective  battering  range  of  the 
guns  mounted  in  the  forts.  Under  such  conditions  groups  of  large  sea 
mines  to  be  fired  by  observation  should  be  scattered  irregularly  in  this 
zone.  Mines  fired  by  contact  arrangements  would  probal)ly  soon  become 
useless  in  such  exposed  positions. 

Cherbourg  may  be  taken  as  an  example  of  an  important  town  and 
dockyard  much  exposed  to  an  attack  by  bombardment.  The  naval  yard, 
docks,  and  basins,  cover  an  area  1400  by  900  yards,  and  the  breakwater 
on  which  the  most  advanced  forts  are  situated  is  only  1900  yards  to 
the  front. 

Assuming  that  the  artillery  mounted  in  these  forts  possess  a  battering 
range  of  3000  yards,  it  is  evident  that  the  vessels  of  a  foe  can  lie  out- 
side this  range  and  destroy  the  dockyard  by  deliberate  bombardment. 
A  fleet  possessing  the  power  to  execute  such  an  undertaking  is  not  to 
be  baulked  by  torpedo  boats  and  small  fry  of  that  kind,  but  a  number 
of  large  mines  placed  in  these  advanced  waters  would  l)e  of  priceless 
value  to  the  defenders. 

The  attacking  forces  would  then  be  compelled  either  to  undertake 
the  protracted  operations  required  for  the  destruction  of  the  mines,  or 
to  run  a  great  risk  of  destruction  themselves.  In  the  former  case 
sufficient  time  might  be  gained  l)y  the  defence  to  summon  a  relieving 
force  by  sea ;  and  in  the  latter,  the  results  might  be  felt  throughout 
the  war. 

Fig.  85  on  the  next  page  gives  a  sketch  plan  of  tlie  arrangements 
which  could  ])e  made.  The  mines  are  arranged  in  seven  groups,  each 
containing  seven  mines,  and  each  mine  fi)'cd  singly  by  observers  situated 
in  two  stations  A  and  B ;  the  latter,  upon  which  the  mines  in  each 
group  are  directed,  is  situated  on  a  hill  230  ft.  liigh,  near  the  town  of 
Heneville,  on  the  left  of  the  position.  The  former,  on  the  extreme 
right  of  the  position,  is  on  high  ground,  near  the  quarries  of  Becquet. 
The  stations  are  separated  by  a  direct  distance  of  9000  yards,  and  the 
most  distant  of  these  outer  or  advanced  mines  are  about  13,000  yards 
from  station  A,  and  the  nearest  about  8000  yards  oft".  All  these  mines 
can  be  l)rought  closer  in  if  so  desired.  On  days  when  the  dockyard 
could  be  seen  at  bombarding  range,  the  masts  of  the  vessels  could  also 
be  seen  from  the  stations  through  the  telescopes  of  the  observing  instru- 
ments, and  the  most  distant  mines  could  be  fired  accurately  if  the 
instruments  are  well  made,  fixed,  and   served.     The  observers  bi'im:;  on 


To  face  page  170. 


Defence  of  Cherlxni/rg.  171 

high  ground,  are  enabled  to  see  at  once  wliere  a  vessel  iloats,  approxi- 
mately, and  the  plane  table  gives  them  the  necessary  information 
concerning  the  mines.  Moreover,  the  groups  are  so  arranged  that  no 
two  mines  and  no  two  groups  are  intersected  by  the  same  line  of  sight 
from  station  A.  The  defect  which  the  opponents  to  double  observation 
firing  make  so  much  fuss  about  is  thereby  obviated.  The  arrangement 
is,  I  believe,  novel,  but  is  only  possible  when  there  is  a  large  area  to  be 
mined  by  a  small  number  of  groups. 

A  seven-cored  electric  cable  connects  the  two  firing  stations.  It  is 
led  on  plan  across  the  harbour  and  behind  the  breakwater.  The 
sea  "  earth  "  common  to  the  system  would  be  taken  from  B,  and  one 
core  for  each  alignment  would  be  normally  "  earthed  "  at  B  through 
a  high  resistance,  and  a  sensitive  galvanometer.  The  other  cores  of 
the  multiple  cable  would  be  spare,  and  one  would  be  required  for 
telephonic  communication  between  A  and  B. 

At  A  the  sweep  arm  of  the  telescope  would  be  so  constructed  as  to 
make  contact  with  a  series  of  small  metal  arcs  fixed  on  the  plane  table, 
each  covering  the  angle  subtended  at  A  by  one  group  of  mines.  These 
metal  arcs  would  be  in  connection  with  the  cores  for  alignments,  carried 
to  B,  and  a  signal  current  would  pass  through  the  high  resistance  to 
earth  at  B  whenever  the  sweep  arm  at  A  touched  one  of  these  small 
metal  arcs.  In  this  manner  the  observer  at  B  would  immediately  know 
what  group  or  groups  of  mines  the  instrument  at  A  was  directed  upon, 
and  this  although  the  alignment  is  itself  directed  upon  B. 

The  observer  at  B  would  deal  with  the  same  alignment,  or  group 
line,  until  the  galvanometer  ceased  to  deflect,  and  in  this  manner  it 
would  be  hardly  possible  for  the  two  observers  to  be  looking  at  different 
vessels.  The  other  actions  would  be  similar  to  the  operations  of  double 
observation  firing  already  described  on  pages  150  to  153,  except 
that  firing  by  means  of  metal  buttons  on  the  plane  table  would  not  be 
accurate  enough  for  such  long  ranges,  and  it  would  be  necessary  to 
construct  the  in-strument  at  A  like  a  large  theodolite  with  a  carefully 
graduated  horizontal  circle  and  vernier  adjustment.  The  telescope 
could  then  be  clamped  with  its  arm  on  each  mine  button  in  succession, 
and  its  line  of  collimation  dii'ected  exactly  on  the  mine.  On  a  vessel 
covering  the  latter  the  mine  would  be  fired  as  soon  as  the  foremast 
came  upon  the  cross-hairs  of  the  telescope.  In  order  to  assist  the 
observer  at  A  in  this  operation,  the  mines  should  not  be  moored  too 
close  together.  On  the  diagram  they  are  shown  at  intervals  of  one  and 
a  half  cables,  or  300  yards. 

The  depth  of  water  does  not  exceed  26  fathoms  at  the  most  distant 
portions  of  this  advanced  mine  field,  and  most  of  the  mines  are  situated 


Defence  of  Cherbourg.  171 

hicli  ground,  are  enabled  to  see  at  once  where  a  vessel  floats,  approxi- 
mately, and  the  plane  table  gives  them  the  necessary  information 
concerning  the  mines.  Moreover,  the  groups  are  so  arranged  that  no 
two  mines  and  no  two  groups  are  intersected  by  the  same  line  of  sight 
from  station  A.  The  defect  which  the  opponents  to  double  observation 
firing  make  so  much  fuss  about  is  thereby  obviated.  The  arrangement 
is,  I  believe,  novel,  but  is  only  possible  when  there  is  a  large  area  to  be 
mined  by  a  small  number  of  groups. 

A  seven-cored  electric  cable  connects  the  two  firing  stations.  It  is 
led  on  plan  across  the  harbour  and  behind  the  breakwater.  The 
sea  "  earth "  common  to  the  system  would  be  taken  from  B,  and  one 
core  for  each  alignment  would  be  normally  "earthed  "at  B  through 
a  high  resistance,  and  a  sensitive  galvanometer.  The  other  cores  of 
the  multiple  cable  would  be  spare,  and  one  would  be  required  for 
telephonic  communication  between  A  and  B. 

At  A  the  sweep  arm  of  the  telescope  would  be  so  constructed  as  to 
make  contact  with  a  series  of  small  metal  arcs  fixed  on  the  plane  table, 
each  covering  the  angle  subtended  at  A  by  one  group  of  mines.  These 
metal  arcs  would  be  in  connection  with  the  cores  for  alignments,  carried 
to  B,  and  a  signal  current  would  pass  through  the  high  resistance  to 
earth  at  B  whenever  the  sweep  arm  at  A  touched  one  of  these  small 
metal  arcs.  In  this  manner  the  observer  at  B  would  inmiediately  know 
what  group  or  groups  of  mines  the  instrument  at  A  was  directed  upon, 
and  this  although  the  alignment  is  itself  directed  upon  B. 

The  observer  at  B  would  deal  with  the  same  alignment,  or  group 
line,  until  the  galvanometer  ceased  to  deflect,  and  in  this  manner  it 
would  be  hardly  possible  for  the  two  observers  to  be  looking  at  different 
vessels.  The  other  actions  would  be  similar  to  the  operations  of  double 
observation  firing  already  described  on  pages  150  to  153,  except 
that  firing  by  means  of  metal  buttons  on  the  plane  table  would  not  be 
accurate  enough  for  such  long  ranges,  and  it  would  be  necessary  to 
construct  the  instrument  at  A  like  a  large  theodolite  with  a  carefully 
graduated  horizontal  circle  and  vernier  adjustment.  The  telescope 
could  then  be  clamped  with  its  arm  on  each  mine  button  in  succession, 
and  its  line  of  collimation  directed  exactly  on  the  mine.  On  a  vessel 
covering  the  latter  the  mine  would  be  fired  as  soon  as  the  foremast 
came  upon  the  cross-hairs  of  the  telescope.  In  order  to  assist  the 
observer  at  A  in  this  operation,  the  mines  should  not  be  moored  too 
close  together.  On  the  diagram  they  are  shown  at  intervals  of  one  and 
a  half  cables,  or  300  yards. 

The  depth  of  water  does  not  exceed  26  fathoms  at  the  most  distant 
portions  of  this  advanced  mine  field,  and  most  of  the  mines  are  situated 


172  Sv.bmarine  Mining. 

in  from  15  to  20  fathoms.  Those  in  less  than  15  fathoms  can  he  ground 
mines  containing  900  lb.  of  blasting  gelatine,  and  the  remainder  can  be 
500  lb.  buoyant  mines  moored  on  a  span  so  as  to  be  submerged  about 
7  fathoms  below  low-water  level.  The  cases  to  be  employed  and  other 
particulars  are  given  on  pages  80  to  88.  The  diameter  of  the  effective 
circle  of  each  mine  would  thus  be  at  least  60  ft. 

It  does  not  often  occur  that  advanced  mines  play  so  important  a  part 
in  the  defence  of  a  sea  fortress,  because  nations  seldom  place  large  arsenals 
in  such  exposed  positions.  When  they  do  so,  and  spend  enormous  sums 
on  fortifications  and  armaments  which  are  powerless  to  prevent  bom- 
bardment, it  becomes  necessary  to  spend  money  freely  on  advanced 
mines.  The  system  described  would  cost  say  20,000^.,  which  would  be 
reduced  by  nearly  1-1:,000/.  if  the  same  number  of  mines  on  the  contact 
system  were  employed  in  place  of  the  large  observation  mines,  the  saving 
being  principally  eftected  by  the  use  of  single  cable  instead  of  multiple 
cable,  and  these  mines  would  be  dangerous  to  a  foe  at  night,  whereas 
the  observation  mines  could  not  be  worked  by  night  at  such  long  range. 

However,  as  before  stated,  the  employment  of  contact  mines  cannot 
be  recommended  in  such  exposed  positions,  and  where  the  tidal  currents 
are  strong  and  the  waters  turbulent.  Such  mines  would  probably  not 
remain  long  in  good  order,  and  repairs  might  soon  become  impossible  in 
the  advanced  mine  field  if  the  defenders  were  weaker  than  their  foe  on 
the  open  sea. 

Semi-Advanced  Mines. — A  few  mines  in  advance  of  the  forts,  and 
within  their  efiective  battering  range,  should  seldom  be  omitted  in  the 
defence  of  any  important  sea  fortress.  The  knowledge  or  the  suspicion 
of  their  presence  in  such  situation  impedes  the  action  of  an  attacking 
force  immensely  ;  and  if  any  attempt  be  made  to  clear  a  channel  by 
countermining,  it  has  to  be  commenced  from  afar,  and  conducted  for  a 
considerable  distance,  with  an  enormous  expenditure  of  explosive  ma- 
terial, and  by  operations  so  tedious  and  dangerous  as  to  invite  disaster. 
But  we  must  not  anticipate.  Countermining  is  now  considered  so 
important  a  means  of  attack  (whether  correctly  or  not)  that  it  deserves 
something  more  than  a  passing  remark,  and  shall  be  dealt  with  in 
another  page.  If  countermining  be  not  resorted  to,  or  the  mines  ren- 
dered inoperative  by  other  means,  it  is  evident  that  a  fleet  attacking  at 
battering  range  must  come  to  an  anchor,  or  verily  the  vessels  would 
"  incur  numerous  nautical  dangers  "  (Lefroy). 

A  group  of  seven  large  mines  fired  by  observation  is  shown  in  the 
Passe  de  I'Ouest.  They  are  moored  in  from  8  to  10  fathoms,  and  may, 
therefore,  be  ground  mines  containing  GOO  lb.  of  blasting  gelatine,  an 
effective  circle  on  the  surface  of  lather  over  30  ft.  radius  being  tliei-('l)y 


Cherbouvf)  continued.  ^7^ 

obtained.  The  mines  in  this  group  could  not  act  by  contact  for  reasons 
ah-eady  stated  with  reference  to  the  advanced  mines,  and  in  addition 
because  they  would  impede  the  traffic  of  the  French  vessels. 

The  mines  are  therefore  spaced  at  about  one  and  a  half  cable  intervals, 
and  are  designed  to  be  fired  by  observation  from  station  B,  a  cable  core 
being  taken  to  an  auxiliary  station  C  on  the  semaphore  hill  at  Querquc- 
ville,  and  visual  signals  may  be  used  if  the  electric  communication  should 
fail  between  B  and  C.  The  firing  arrangements  may  be  one  of  those 
described  on  pages  150  to  153,  say  one  of  the  lines  on  Fig.  78. 

More  than  one  group  of  semi-advanced  mines  would  probably  be  em 
ployed,  but  the  group  shown  as  an  example  is  sufficient  to  indicate  the 
practice  to  be  pursued. 

il/me  Blocks. — The  anchorage  and  dockyard  of  a  great  naval  arsenal 
like  Cherbourg  must  also  be  secured  as  far  as  possible  against  direct 
capture  by  a  fleet.  Powerful  guns  mounted  in  armoured  forts  and 
shore  batteries  form  the  chief  defence,  but  they  can  be  passed  by  first- 
class  ironclads  unless  obstructions  of  some  kind  are  added  to  delay  the 
passage  of  vessels  up  important  channels.  The  best  obstructions  are 
submarine  mines,  and  when  well  protected  both  by  heavy  artillery  and 
by  quick-firing  guns,  the  defence  to  prevent  passage  then  becomes  so 
powerful,  and  the  operations  necessary  to  force  passage  become  so  diffi- 
cult, tedious,  and  dangerous  that  we  may  feel  sure  they  will  not  often 
be  attempted. 

When  mines  are  employed  in  this  way,  they  form  what  is  termed  a 
mine  block,  and  it  is  usual  to  leave  certain  portions  free  of  contact 
arrangements,  so  that  friendly  vessels  may  pass  and  repass  without 
injuring  the  mines.  These  channels  should,  however,  be  closed  to  the 
vessels  of  a  foe  by  mines  at  a  lower  level,  either  ground  or  buoyant 
(according  to  the  depth  of  water),  and  fired  by  observation.  A  channel 
thus  mined  is  absolutely  blocked  so  long  as  the  system  remains  in  good 
order,  but  a  mine  block  is  somewhat  vulnerable  to  attack  by  counter- 
mining, because  the  position  of  the  mine  block  may  generally  be  guessed 
with  an  approach  to  absolute  certainty.  For  instance,  at  Cherbourp-,  if 
used  at  all,  the  blocks  must  exist  in  the  waters  between  He  Pelee  and  the 
Fort  de  I'Est  at  one  end  of  the  breakwater,  and  in  the  water  between 
the  Fort  de  I'Ouest  and  the  western  mainland  on  the  other  side.  The 
fact  that  such  mine  blocks  can  be  quickly  pierced  by  countermining 
produces  a  want  of  confidence  in  their  efficiency,  and  inasmuch  as  they 
are  frequently  very  costly,  owing  to  the  large  number  of  mines  required, 
the  advisability  of  using  tliem  in  a  situation  such  as  the  western 
entrance  to  Cherbourg  is  open  to  question.  It  may  be  far  better  to 
use    the    same    mines    scattered  irregularly    in    waters  further    to  the 


174  Subviarine  Mining. 

front,  the  semi-advanced  mines  being  reinforced  and  the  absolute  block 
sacrificed. 

However,  mine  blocks  are  the  fashion,  and  we  must  therefoie 
describe  them. 

By  referring  to  the  diagrams  of  Cherbourg,  it  will  be  seen  that  the 
design  for  a  mine  block  on  the  eastern  side  consists  of  two  rows  of 
ground  mines  fired  by  observation  from  Fort  Imperial,  whence  the 
electric  cables  are  led.  The  front  row  of  seven  mines  in  5  to  6  fathoms 
may  be  formed  with  400  lb.  charges  spaced  at  intervals  of  about  half 
a  cable.  The  row  is  aligned  between  the  outer  buoy  and  the  Fort  de 
I'Est,  whence  an  observer  signals  to  the  Fort  Imperial.  The  inner  and 
similar  row  of  mines  is  aligned  between  the  buoy  oQ"  Trinity  Point  and 
the  Fort  de  I'Est.  Behind  these  lines  are  placed  three  or  more  groups, 
each  of  five  electro-contact  mines  in  two  rows,  directed  upon  Fort 
Imperial  for  facility  in  laying.  They  are  spaced  at  about  200  ft. 
intervals,  and  can  carry  charges  of  70  lb.  to  100  lb.  as  considered 
expedient.  The  electric  cables  from  these  mines  are  also  led  into  Fort 
Imperial. 

It  will  be  noticed  that  these  mines  are  so  situated  as  to  be  protected, 
as  far  as  possible,  by  the  breakA\ater  and  by  the  He  Pelee.  They  are, 
in  fact,  sheltered  from  all  except  north-westerly  gales.  It  is  assumed 
that  powerful  electric  search  lights  are  mounted  on  these  forts. 

As  the  electric  cables  from  the  advanced  mines  converge  on  the  Fort 
de  I'Est,  and  are  carried  thence  to  the  shore  near  the  Greves  battery,  it 
is  necessary  to  prevent  boats  from  attacking  same  by  creeping  operations 
under  the  cover  of  darkness.  For  this  purpose  a  passive  obstruction 
consisting  of  heavy  cribs  of  timber  filled  with  stones  should  be  placed 
so  as  to  connect  the  Pont  de  I'lleand  the  mainland  at  "  la  vielle  beacon." 
Greves  battery  should  also  be  strengthened  to  resist  capture  by  surprise, 
and  some  quick-firing  guns  be  mounted  therein  on  disappearing  carriages. 
This  is  most  important.  At  present  quick-firing  guns  are  mounted  on 
land  as  they  are  on  ship,  upon  fixed  stands,  and  consequently  both  guns 
and  stands  would  be  easily  destroyed  by  the  preliminary  artillery  fire 
that  should  prepare  the  way  for  any  night  expedition  of  the  kind.  If 
the  quick-firing  guns  were  mounted  on  disappearing  carriages,  neither 
guns  nor  carriages  need  be  exposed  or  their  presence  known  until  the 
time  arrived  for  using  them.  I  pointed  this  out  immediately  after  the 
operations  at  Langston  Harbour  last  year  ;  as  also  the  absolute  necessity 
to  employ  smokeless  powder  for  these  (juick-firing  guns. 

Observing  station  A  should  be  protected  by  a  small  field  work  with 
wire  entanglements  and  other  obstacles,  and  the  same  applies  to  stations 
B  and  0  on  the  west.      Here  tlic    mine    block   mav  consist  of   two  rows 


Glicrhuarg  continued.  175 

of  ground  mines  in  from  4  to  8  fathotns,  and  containing  charges 
sufficient  to  produce  eflfective  surface  circles  of  30  ft.  radius.  The  mines 
may  be  spaced  at  half-cable  intervals,  and  be  fired  from  station  B, 
whence  the  electric  cables  would  be  led.  The  rows  converge  on  station 
C  where  an  observer  would  signal  to  B  when  a  vessel  crossed  one  or 
other  of  the  rows  of  mines.  Or  the  signals  may  be  made  from  Fort 
Chavagnac  which  exists  upon  the  alignments.  A  cable  core  is  taken  to 
the  fort  for  tliis  purpose  from  the  multiple  main  cable  leading  to  the 
semi-advanced  group.  The  shallower  waters  between  the  3  and  5 
fathom  lines  are  closed  by  a  group  of  seven  electro-contact  mines,  the 
firing  being  under  control  from  station  B.  It  will  be  noticed  that  a 
small  space  of  unmined  water  exists  between  the  observation  and  the 
electro-contact  mine.  This  is  unavoidable,  because  the  former  destroy 
the  latter  if  placed  too  close  to  them.  The  electric  cables  from  this 
mine  block  are  led  across  waters  which  are  not  required  for  anchorage, 
and  they  are  protected  both  by  the  forts  in  front  and  by  the  mines 
themselves. 

The  junction  box  for  a  group  of  mines  should  be  situated  as  near  to 
the  mines  as  possible,  both  to  economise  electric  cable,  and  to  facilitate 
repairs.  When  two  or  more  rows  of  mines  are  close  together,  the 
junction  boxes  can  be  placed  as  shown  on  the  design  for  the  left  mine 
block,  but  when  the  mines  are  arranged  in  single  rows  the  arrangement 
shown  on  diagram  for  the  advanced  and  semi-advanced  mines  must  be 
followed.  The  general  sea  defence  of  a  fortress  like  Cherbourg  resolves 
itself  into  : 

1.  The  protection  of  the  dockyard  and  town  from  capture  or  bom- 
bardment. 

2.  The  protection  of  the  anchorage. 

Not  only  is  Cherbourg  extremely  vulneraljle  to  bombardment,  but  it 
possesses  another  weak  point,  enabling  an  active  foe  to  capture  it  by 
assault  without  bringing  a  single  vessel  inside  the  breakwater.  The 
precise  metliod  need  not  l)e  further  alluded  to,  except  to  note  that  the 
same  mines  which  throw  difficulties  in  the  way  of  bombardment,  would 
also  increase  the  dangers  run  by  vessels  assisting  in  the  operation  of 
an  attempt  at  capture  by  assault.  The  anchorage  may  be  considered 
secure ;  the  powerful  forts  in  front  of  it  sweep  with  their  guns,  at  what 
may  now  be  considered  short  ranges,  the  waters  within  engaging  distance 
of  the  roadstead,  and  make  it  highly  improbable  that  any  foe  would 
send  a  fleet,  or  any  portion  thereof,  into  a  position  of  such  nautical 
danger  until  the  defence  had  been  broken  down  l)y  the  capture  or  de- 
struction of  some  of  the  foi-ts  and  batteries.  As  regards  boat  attacks, 
or  what  will  in  future  take  the  place  of   the  old  cutting-out  expeditions. 


176  Submarine  Mining. 

sea  mines  are  not  likely  to  hinder  them  niucli.  Two  or  three  boats 
might  Come  to  grief,  but  the  remainder  would  get  through,  and  be  able 
(if  not  met  by  other  boats)  to  attack  vessels  in  the  anchorage.  The 
only  trustworthy  defence  of  vessels  at  anchor  against  boat  attack  is 
boat  defence,  aided,  as  it  would  be  by  search  lights  and  quick-firing 
guns  both  from  ships  and  forts. 

Reverting  to  the  sea-mining  design  for  Cherbourg,  it  will  be  noticed 
that  it  is  proposed  to  employ  large  mines  fired  by  observation  rather 
than  electro-contact  mines.  Reasons  have  already  been  given  for  this 
choice  in  the  open  waters  ;  but  contact  mines  are  the  general  favourites, 
especially  for  the  principal  mine  blocks.  The  preference  usually  shown 
for  contact  mines  is  not  easily  accounted  for.  On  the  contrary,  these 
mines  are  so  local  in  their  action,  that  modern  men-of-war  with  their 
numerous  water-tight  compartments  are  more  likely  to  succumb  to  the 
racking  blow  of  a  large  mine.  Moreover,  the  principal  mine  fields  are 
usually  placed  precisely  where  it  is  best  to  provide  for  locomotive 
torpedoes  of  the  Brennan  or  similar  types,  and  such  weapons  can  be 
used  over  waters  sown  with  observation  mines,  but  not  over  waters 
sown  with  contact  mines. 

Leaving  Cherbourg,  where  advanced  mines  are  so  valualile,  we  will 
now  turn  to  an  example  in  which  the  mines  should  be  placed  in  retired 
positions.  The  great  city  and  harbour  of  New  York  may  be  taken  as 
a  case  in  point. 


177 


CHAPTER  XV. 

Designs  for  Mine  Defence. 
Dockyards  where  men-of-war  are  built  should  be  secure  from  attack, 
and  should  therefore  be  situated  many  miles  up  a  tortuous  river  or  inlet 
difficult  to  navigate  at  the  best  of  times.      Chatham  is  a  practical  example 
of  this  ideal. 

The  protection  of  large  commercial  shipping  centres  from  purely  naval 
attacks  is  easily  effected  if  they  be  similarly  situated.  The  great  cities 
of  London  and  New  York  are  typical  cases.  It  is  not  desirable  that 
our  own  defences  should  be  discussed  in  detail,  especially  by  one  who 
for  many  years  was  engaged  upon  them  at  our  War  Office.  New  York 
will,  therefore,  be  selected,  and  a  design  for  the  sea  mine  defence  will  be 
drawn  up  and  described. 

The  position  of  the  mine  fields  should  be  retired  from  the  open  sea 
both  because  they  would  then  be  more  difficult  to  approach,  and  because 
the  shelter  would  enable  the  miner  to  carry  out  the  mooring  operations 
in  rough  weather.  Care  must,  however,  be  taken  to  moor  some  of  the 
mines  at  or  a  little  beyond  the  limits  of  bombarding  range,  and  the 
remainder  should  be  scattered  in  groups  or  fields  as  irregularly  as  may 
be  compatible  with  their  protection  by  light  artillery,  and  especially 
quick-tiring  guns  mounted  in  proper  emplacements. 

Absolute  mine  blocks  which  are  so  fashionable,  with  their  floating 
impediments  telling  a  foe  where  the  mines  are  laid,  should  be  avoided. 
This  method  places  too  many  eggs  in  one  basket,  and  shows  the 
position  of  the  basket.  A  mine  defence  should  be  deep  and  narrow  in 
plan,  rather  than  wide  and  shallow  3  and  the  centre  of  each  channel 
should  be  mined  more  than  the  sides. 

Mines  should  extend  right  through  the  defence,  to  the  very  last 
entrenchment.  Sir  Lintorn  Simmons  once  said,  "  A  gun  for  the  defence 
which  can  be  reserved  until  the  attack  is  in  the  last  period  is  worth  any- 
thing" (R.E.  Papers,  vol.  xviii.,  1870) ;  and  the  same  remark  applies  to 
mines.  In  a  letter  to  the  Times,  1855,  signed  "  B.,"  and  attributed  to 
the  late  Sir  John  Burgoyne,  we  read,  "  one  of  the  principal  ingredients 
in  defensive  works  is  an  obstacle  to  the  approach  of  the  assailants." 
n 


178  Sidmiavine  Mining. 

On  this  principle  mines  should  be  moored  so  as  to  help  the  forts  when 
they  are  attacked,  by  obstructing  those  portions  of  the  channel  outside 
the  forts  at  engaging  distances. 

Small  side  channels  that  are  not  required  by  the  defenders  may  be 
blocked  by  passive  obstruction  or  mechanical  mines,  especially  if  these 
side  channels  are  likely  to  prove  of  use  to  a  foe  in  delivering  boat 
attacks.     Let  us  apply  these  principles  to  our  example.  New  York. 

This  magnificent  emporium  of  trade,  whence  radiate  the  pulsating 
arteries  essential  to  the  life  of  one  of  the  greatest  civilised  nations  the 
world  has  ever  seen,  is  situated  on  a  peninsula  on  the  left  bank  of  the 
River  Hudson,  and  is  covered  from  the  open  sea  by  the  end  of  Long 
Island,  between  which  and  Staten  Island  the  Hudson  flows  through  the 
Narrows  into  an  estuary  about  seven  miles  square  (49  square  miles) 
containing  several  channels  divided  irregularly  by  large  banks  with 
about  two  fathoms  over  them  at  low  tide. 

Long  Island,  about  100  miles  by  17,  covers  a  large  sound  or  arm  of 
the  sea,  over  20  miles  wide,  that  separates  the  island  from  the  States  of 
Connecticut  and  New  York.  At  a  distance  of  12  miles  from  tlie  city 
tills  sound  narrows  down  to  a  width  oi  Ih,  miles,  and  at  8  miles  from 
the  city  it  is  only  |  mile  wide.  Here  two  forts,  one  at  Willet's  Point 
on  Long  Island,  the  other  at  the  extremity  of  Throg's  Neck,  on  the 
opposite  shore,  protect  the  channel,  which  from  this  point  inwards  is 
called  the  East  River.  Its  width  is  still  further  reduced  as  it  approaches 
the  city,  until  finally  at  Hell  Gate  it  is  less  than  a  \  mile  wide. 

Long  Island  thus  protects  the  city  from  the  sea,  obliging  any  naval 
attack  to  be  delivered  on  one  or  other  of  two  intricate  paths  of  approach. 
But  the  defence  of  an  island  against  a  foe  who  possesses  the  conmiand 
of  the  sea  is  much  more  difficult  than  is  that  of  tlie  main  land  of  a 
country  held  by  a  courageous  people  and  intersected  by  numerous  lines 
of  communication.  Long  Island,  therefore,  is  at  one  and  the  same 
time  a  source  of  protection  and  a  source  of  weakness.  It  gives  strength 
to  resist  a  purely  naval  attack,  but  is  very  vulnerable  to  a  combined 
naval  and  military  operation. 

In  these  days  it  is  impossible  to  prevent  troops  landing  when  the 
operation  is  covered  by  a  fleet,  and  it  is  also  impossible  to  check  their 
advance  so  long  as  they  advance  in  a  parallel  line  and  M-ithin  the  effec- 
tive range  of  its  artillery. 

New  York  is  open  to  capture  by  an  operation  of  this  nature,  a  strong 
force  landing  on  Long  Island  from  the  Sound  as  near  to  the  city  as 
possible,  and  advancing  by  the  East  River  shore,  under  the  covering 
protection  of  a  fleet,  and  assisting  the  ships  by  capturing  the  batteries 
or  mining  stations  on  that  shore,  which  would  thus  be  taken  in  reverse 


Defence  Scheme  for  Neiv  York.  179 

With  Long  Island  in  its  present  defenceless  state  such  an  operation 
would  be  quickly  done,  in  spite  of  submarine  mines,  dynamite  guns, 
plunging  Davids,  and  what  not.  To  describe  a  possible  coup  de  main 
is  to  suggest  a  defence,  and  our  cousins  might  do  worse  than  spend  some 
of  their  annual  surplus  in  the  construction  of  a  string  of  forts  between 
Jamaica  Bay  and  East  River.  Taking  things  as  they  exist,  the  follow- 
ing arrangement  of  mines  would  give  a  strong  defence  to  East  River 
against  a  purely  naval  attack.  In  order  to  hamper  any  attack  on  Fort 
Schuyler  the  navigable  water  to  the  west  of  Hewlett  Point  and  Elm 
Point  should  be  mined.  For  reasons  already  stated,  the  firing  stations 
should  not  be  located  on  Long  Island,  but  on  the  opposite  side.  Ground 
mines  can  be  used  in  front  of  the  forts,  and  be  charged  with  600  lb.  or 
900  lb.  of  blasting  gelatine  according  to  the  depth  of  water  (see  pages 
SO  and  83.)  The  principal  firing  station  may  be  situated  to  the  north- 
west of  Fort  Schuyler,  near  enough  to  be  under  the  protection  of  the 
fort,  and  far  enough  to  be  clear  of  its  smoke  and  of  the  fire  which  it 
draws  upon  it. 

An  auxiliary  observing  station  may  be  placed  at  M  (see  Fig.  80),  or 
further  from  the  shore  if  M  be  considered  too  exposed  to  attack  by  a 
party  landing  from  boats  at  high  tide.  But  its  position  ought  to  be 
screened,  and  should  not  be  known  to  a  foe,  and  this  remark  applies  to 
every  observing  station  used  in  connection  with  sea  mines. 

The  mines  are  shown  as  moored  in  four  lines  converging  on  M,  and 
the  cables  would  be  carried  to  the  back  of  Throg's  Neck  to  the  observ- 
ing station  at  that  place  ;  this  would  connect  with  M  by  means  of  a 
three-cored  cable,  two  cores  being  required  for  observing  and  one  for 
telephoning.  Lines  1  and  3  would  be  operated  from  one  of  the  writer's 
plane  table  observing  arcs,  lines  2  and  4  from  another,  and  there  would 
be  an  observer  to  each  core  at  M,  who  would  send  a  positive  current  for 
one  alignment,  and  a  negative  for  the  other,  to  the  instrument  shown  on 
Fig.  76,  page  151. 

These  mines  being  spread  over  a  large  expanse  of  water  would  be 
most  useful  against  vessels  that  might  engage  the  forts  at  battering 
ranges. 

The  water  to  N.  of  Willet's  Point  could  also  be  mined  similarly,  but 
Throg's  Neck  is  a  position  excellently  well  adapted  for  a  battery  of 
dynamite  guns  tiring  both  to  front  and  rear,  in  which  event  the  waters 
within  a  radius  of  a  mile  can  be  kept  clear  of  mines. 

In  nearly  every  defence  some  of  the  side  channels  are  a  source  of 
weakness.  They  should  be  blocked  by  mechanical  mines,  or  by  passive 
obstructions,  or  both  combined.  Thus  two  groups  of  mechanical  mines 
may  be  placed  between  City  Island  and   Rodman's  Neck,  if  other  cou- 


180 


Submarine  Mining. 


siderations  do  not  proliil)it  same,   and   another  group  may  be  placed  off 
the  rocks  at  Elm  Point. 

Abreast  of  Fort  Schuyler  a  mine  field  may  be  formed  consisting  of 
four  groups  of  electro-contact  mines  Hanking  a  fairway,  mined  with 
several  pairs  of  observation  ground  mines.     This  fairway  can  be  in- 


5i- 

i^y*. 

f> 

v> 

\ 

" 

p 

m 

r'r 

'' 

Ju^SU 

Mg.8€. 


clined  so  that  its  line  of  direction  falls  on  Willet's  Point,  and  each  paii- 
of  mines  would  be  fired  from  the  central  station  at  Throg's  Neck  when 
a  vessel  came  on  the  observed  intersection.  One  of  the  writer's  plane 
table  arcs  might  be  employed  for  this  work. 

These  portions  of  the  defence  may  collapse  after  due  resistance,  and 
(jther  iiiino  fields  in   rear  should  thi-refore  be  provided.      One   can   be 


Neiif  York  continued  181 

placed  at  Old  Ferry  Point,  another  at  Olawson  Point,  and  still  another 
perhaps  at  the  Brothers,  each  having  a  narrow  fairway  free  of  contact 
mines. 

An  attacking  squadron  that  succeeded  in  forcing  its  way  to  the 
Brothers  would  be  within  shelling  distance  of  the  city,  and  terms  would 
prol)al)ly  be  arranged  to  prevent  further  operations. 

Let  us  now  turn  to  the  principal  commercial  entrance  to  New  York 
Harljour. 

The  attacking  forces  would  here  meet  with  numerous  nautical  diffi- 
culties. The  deepest  water  over  the  bar  is  but  3|  fathoms  at  low 
water,  and  the  rise  of  tide  at  springs  is  less  than  one  fathom — total, 
22  ft.  6  in.  at  low  and  28  ft.  6  in.  at  high  water.  First-class  ironclads 
should  therefore  keep  outside,  and  any  attack  on  this  side  must  be 
made  by  war  vessels  of  smaller  draught.  The  channels  inside  the  bar 
are  intricate,  and  skilled  local  pilots  are  required  to  take  steamers  into 
port.  If  some  of  the  buoys  and  light  vessels  were  only  slightly  shifted 
the  navigation  of  vessels  would  be  made  so  difficult  to  strangers  as  to 
be  well-nigh  prohibitive.  Moreover,  the  land  is  so  distant  and  so  hard 
to  approach,  owing  to  the  flats  that  extend  for  miles  in  front  of  it,  that 
a  simultaneous  attack  by  land  could  receive  no  assistance  from  the 
forces  afloat.  Combined  operations  like  those  suggested  for  the  advance 
up  the  East  River  are  therefore  impossible. 

Considering  these  things,  it  certainly  appears  that  New  York,  like 
some  other  places,  has  a  weak  back  entrance  and  a  strong  front  door. 
Yet  an  attack  vid  Sandy  Hook  and  the  Narrows  seems  to  be  feared 
more  than  one  in  the  other  direction,  if  one  may  judge  from  the  fortifi- 
cations now  existing,  especially  at  the  Narrows. 

The  writer  believes  that  the  key  of  the  lock  for  securing  the  main 
entrance  to  New  York  Harbour  will  be  found  at  the  inner  end  of  the 
sandbank  called  the  Dry  Romer.  This  is  ten  miles  from  the  nearest 
point  of  the  city  and  eight  from  Brooklyn.  The  Narrows  are  only  six 
miles  from  the  city  and  four  from  Brooklyn,  and  vessels  lying  outside 
would  be  within  bombarding  distance  of  them  both.  Every  effort  should 
therefore  be  made  to  present  an  efiective  resistance  to  an  attacking 
squadron  before  it  comes  so  far. 

The  Swash  Channel  joins  the  main  channel  close  to  the  north  end  of 
the  Dry  Romer,  the  navigable  water  being  only  1250  yards  wide  at  this 
point.  It  is  bounded  on  the  west  by  the  Staten  Island  flats,  with  an 
average  depth  of  only  two  fathoms  over  them. 

The  East  Channel  is  also  1250  yards  wide  at  the  north  end  of  the 
Dry  Romer.  This  fine  channel,  although  not  much  used  by  commerce, 
has  3^  fathoms  over  the  bar,  and  might  1>e   used  by  the  attack  in  war. 


182  Submarine  Mining. 

as  it  lies  beyond  the  efiective  range  of  Sandy  Hook  Fort.  All  the  rest 
of  the  harbour  entrance  is  forbidden  to  vessels  drawing  more  than  14  ft. 
or  15  ft.,  that  is  to  say,  to  war  vessels  that  would  cross  the  Atlantic. 
An  ironclad  fort  on  the  north  end  of  the  Dry  Romer  would  consequently 
hold  this  entrance  to  New  York,  and  with  additional  certainty  if  mines 
were  placed  in  the  channels  on  either  side  of  it.  As  no  fort  exists  there, 
the  mines  are  all  the  more  necessary,  and  some  makeshift  arrangement 
should  be  devised  both  for  protecting  them  against  boat  attack  and  for 
providing  a  firing  station  as  close  to  them  as  possible.  This  could  be 
done  by  floating  a  strong  iron  hulk  to  the  spot,  and  then  filling  her  with 
sand,  leaving  chambers  on  the  north  side  for  firing  and  obser%-ing 
stations,  and  mounting  quick-firing  guns  on  carriages  disappearing 
through  the  deck,  the  guns  remaining  up  when  in  action,  and  out  of 
sit'ht  and  protected  as  far  as  possible  when  not  in  action. 

The  mines  can  be  arranged  in  various  manners,  and  the  plan  shown 
on  Fif.  87  provides  for  the  main  channel  a  combination  of  electro- 
contact  and  of  observation  mines,  the  latter  being  charged  with  600  lb. 
of  explosive  and  moored  on  the  ground  in  two  lines  converging  upon 
Norton  Point.  They  are  not  placed  directly  across  the  channel,  but 
diao-onally,  and  so  that  the  cross  intersection  firing  may  be  eflfected  from 
the  temporary  station  near  at  hand.  In  this  manner  the  west  part  of 
the  channel  becomes  a  fairway  free  from  contact  mines,  and  available  for 
the  traffic  of  the  port.  A  plane  table  observing  arc  can  be  used,  and  a 
sinc^le  core  would  be  led  to  the  alignment  observing  station  on  Norton 
Point,  a  second  core  would  be  required  for  telephonic  communication, 
and  a  third  core  would  be  held  in  reserve,  as  spare.  A  single  core 
should  be  carried  on  to  Sandy  Hook  Fort,  as  shown,  for  communication, 
and  perhaps  it  may  be  led  into  the  Swash  light  vessel  on  the  way.  The 
East  Channel  can  be  closed  by  four  groups  of  electro-contact  mines. 

In  rear  of  the  Dry  Romer  defence  a  second  series  of  mines  may  be 
moored  in  the  main  channel  off  Norton  Point,  in  order  to  hamper  the 
attack  on  the  Narrows.  These  mines  should  be  scattered  over  a  wide 
area,  and  observation  mines  may  advantageously  be  resorted  to,  because 
vessels  would  not  attack  the  Narrows  at  night.  The  mines  can  be 
charged  with  900  lb.  of  explosive  (the  deptli  being  about  11  fatlioms), 
and  can  be  moored  on  the  ground  in  two  lines  crossing  one  another,  and 
directed,  the  one  on  a  station  near  Fort  Tomkins,  the  other  on  a  station 
near  Fort  Hamilton. 

Still  nearer  to,  and  in  front  of  the  Narrows,  a  further  system  of 
observation  mines  moored  on  the  bottom  in  two  rows  forming  a  re- 
entering angle  can  be  directed  on  tlie  two  stations  last  mentioned,  and 
be  fired  therefrom,  by  double  observation,  one  piano  table  observing  arc 


Neiv  York  continued. 


183 


being  used  at  each  station  and  two  cores  connecting  them  for  firing 
purposes.  A  third  core  of  the  seven-cored  cable  shown  on  the  figure 
can  be  employed  for  telephonic  communication.  Two  more  cores  would 
be  required  for  the  mines  off  Norton  Point,  and  two  cores  would  be 
held  in  reserve  as  spare.     A  group   of  electro-contact  mines  can  be 


Fi^.87.       yf  y^ 

tm  0  100'  I  3000  twit 


5  rathom  /rne(' 


placed  on  each  flank.  The  water  is  somewhat  deep  at  the  Narrows, 
and  the  defence  can  here  be  left  to  artillery  and  torpedo  guns  mounted 
on  the  heights  on  either  side,  and  to  locomobile  torpedoes  actuated  from 
suitable  positions  on  either  shore. 

The  defence  of  New  York  Harbour  offers  a  very  interesting  example 


184  Suhmarhie  Mining. 

of  the  general  ideas  whicli  govern  the  application  of  submarine  mines. 
In  every  large  harbour,  however,  the  possible  permutations  and  combina- 
tions are  numerous,  and  no  two  designs  drawn  up  independently,  even 
by  officers  who  have  been  trained  in  the  same  schools,  are  likely  to  be 
precisely  similar. 

Thus,  in  the  example  before  us,  many  engineers  might  prefer  to  sow 
the  Swash  and  East  Channels  with  mechanical  mines,  and  to  place  a  com- 
plete system  of  electrical  mines  in  the  main  channel  off  Sandy  Hook  Fort, 
friend  and  foe  alike  being  thus  compelled  to  use  this  channel  in  time  of 
war.  Such  an  arrangement  would  be  strong,  and  would  deny  the  lower 
bay  to  a  foe ;  but  the  defence  would  be  somewhat  disconnected,  and  for 
this  reason  would,  I  think,  be  weaker  than  the  one  proposed  and  illus- 
trated on  this  paper.  INIoreover,  inasmuch  as  a  war  may  last  through 
the  winter  months,  and  masses  of  ice  come  down  when  the  Hudson 
River  breaks  up,  mechanical  mines  in  situations  like  the  Swash  would 
certainly  be  destroyed  by  self-ignition  at  such  a  time. 

Coaling  Stations. — The  remarks  already  made  on  the  mine  defence 
plans  for  naval  arsenals  and  for  commercial  harbours  or  rivers,  apply 
also  to  coaling  stations,  except  that  the  positions  of  the  latter  can  be, 
and  generally  are,  so  chosen  that  their  defence  requires  a  much  smaller 
expenditure  on  guns,  mines,  and  garrisons.  A  coaling  station  so  situated 
that  its  defence  would  entail  a  heavy  expenditure,  stands  self-con- 
demned. 

Thus  at  Kingstown,  Jamaica,  the  dockyard  and  coaling  depot  should 
be  withdrawn  from  their  present  exposed  position,  and  be  retired  to  the 
inner  harbour.  Were  this  done,  the  general  defence  would  be  much 
less  costly  and  yet  stronger. 

At  some  stations  it  is  only  necessary  to  provide  for  the  security  of 
the  coal  and  the  appliances  used  in  coaling.  For  such  a  place  the 
following  simple  method  of  defence  has  for  some  years  been  a  favourite 
hobby  of  the  writer's,  and  something  of  the  kind  has  also  been  recom- 
mended by  so  high  and  experienced  an  authority  as  General  Sir  Lintorn 
Simmons,  G.O.B.,  R.E.     The  scheme  consists: 

1.  In  stacking  the  coal  at  a  distance  from  the  water,  and  so  situated 
that  it  could  not  be  damaged  by  the  guns  of  a  hostile  cruiser  or  flying 
squadron. 

2.  In  connecting  same  with  the  harbour  by  a  tramway,  gonorally 
inclined  so  that  the  full  trucks  descending  the  incline  would  draw  the 
empty  trucks  up. 

3.  In  providing  shoots  similar  to  tliose  used  in  Durham,  Northumber- 
land, and  South  Wales,  for  quickly  loading  barges  at  the  end  of  the 
tramway. 


Coaling  Stations,  Coast  Towns,  <(c.  185 

4.  In  covering  these  shoots  by  an  earthwork  to  protect  tliem  from 
hostile  artillery  fire. 

5.  In  providing  special  barges  so  constructed  that  when  scuttled  they 
will  just  sink,  and  thus  be  hidden  from  a  foe  should  he  attack  the 
harbour,  and  yet  be  easily  recovered  when  he  retires. 

The  method  of  coaling  by  means  of  barges  is  strongly  advocated  by 
many  officers  of  the  Royal  Navy  as  preferable  to  all  other  means,  and 
barges  can  certsiinly  be  loaded  in  less  time  at  the  shoots  than  they  would 
take  to  unload  at  the  ships. 

One  or  two  companies  of  infantry  behind  carefully  constructed  field- 
works  would  protect  the  coal  depot  from  any  attack  likely  to  be  delivered 
on  land,  and  the  defence  hardly  requires  a  cannon  or  a  mine.  A  few 
mines  covered  by  quick-tiring  guns  would  add  to  the  defence  at  no  great 
expense,  but  such  addition  is  not  essential.  The  idea  ruling  such  a 
defence  is  to  place  the  objective — the  coal — out  of  the  reach  of  a  cruiser. 
Any  damage  he  can  inflict  on  the  shoots  or  the  tramway  could  be 
repaired  in  a  few  hours,  suitable  material  for  repairs  being  kept  in 
reserve  at  the  depot. 

Even  when  it  is  desired  to  provide  facilities  for  repairing  defects 
in  a  ship's  machinery  or  outfit,  a  great  deal  could  be  done  at  such  a 
depot,  a  fitting  shop  and  store  buildings  being  added ;  also  a  few  strong 
trucks  to  carry  loads  of  10  or  15  tons,  and  a  crane  at  the  water  edge  to 
unload  or  load  a  barge  with  the  special  gear  required.  In  short,  the 
scheme  is  capable  of  expansion,  and  for  distant  stations  in  the  Pacific 
has  many  advantages  to  recommend  it. 

Small  Harbours  to  be  denied  to  a  Foe. — It  is  sometimes  most  important 
to  deny  certain  small  harbours  to  a  foe,  although  during  peace  they 
may  be  of  little  or  no  commercial  value.  For  instance,  the  little 
harbour  of  Balaklava  was  of  immense  strategic  importance,  and  con- 
sidering the  large  sums  spent  upon  the  sea  forts  and  land  defences  of 
Sebastopol,  the  undefended  state  of  Balaklava  was  evidently  an  oversight. 
Marsa  Scirocco,  near  Valetta  is  another  instance — and  others  could  be 
cited. 

Such  harbours  should  evidently  be  dealt  with  so  as  to  put  difiiculties 
in  the  way  of  attacking  forces  that  might  wish  to  utilise  them. 

The  least  expensive  method  would  prol)ably  be  a  defence  by  purely 
automatic  mines  interspersed  with  mines  under  control  from  shore, 
where  a  few  quick-firing  guns  would  aflbrd  a  certain  protection  to  the 
mines  and  to  the  observing  stations  in  connection  with  tliem. 

Open  Roadsteads  and  Coast  Towns. — The  defence  of  towns  located, 
like  Brighton,  on  the  shores  of  the  open  sea  has  been  much  debated  of 
late,  and  there  cannot  be  a  doubt  that  sucli  places  can  only  be  cfiectively 


186  Submarine  Mining. 

protected  by  the  Navy.  In  a  most  excellent  article  in  the  Times  of 
May  25,  1888,  entitled  "The  Higher  Policy  of  Defence,"  the  writer 
truely  said  :  "  The  command  of  certain  waters  exists  when,  within  tliose 
waters,  no  hostile  fleet  can  count  on  the  time  requisite  for  a  serious 
enterprise  without  a  strong  probability  of  having  a  superior  force  to 
deal  with."  Thus,  in  a  single  sentence,  the  only  true  protection  of  our 
coast  towns  from  attack  by  a  fleet  is  clearly  explained.  There  remains 
the  attack  by  one  or  two  swift  cruisers.  The  great  area  of  water  puts 
mining  out  of  the  question,  and  shore  batteries  would  be  useless,  for  the 
bombarding  range  of  a  cruiser  being,  say,  7  or  8  miles,  and  the  extreme 
effective  range  of  guns  on  shore,  firing  at  a  small  rapidly  moving  target, 
being,  say,  3000  yards — it  is  evident  that  the  cruiser  could  remain  out- 
side the  zone  of  fire  of  the  shore  batteries  and  yet  bombard  the  large 
target  ofliered  by  a  coast  town,  so  that  every  shot  would  take  effect. 
Evidently,  therefore,  the  defence  of  such  towns  against  such  attack 
must  be  undertaken  by  guns  afloat.  Wliether  it  is  best  to  place  these 
guns  in  swift  vessels  as  recently  recommended  by  Lord  Armstrong,  such 
vessels  patrolling  the  coast ;  or  whether  it  would  not  be  preferable  to 
mount  them'  on  slower  hulls,  more  heavily  armoured,  each  stationed 
for  its  special  work,  is  a  matter  for  naval  strategists  to  decide. 

Conclusion. — In  conclusion,  as  regards  submarine  mining,  it  is  im- 
portant to  remember  that  each  place  will  form  a  special  problem,  and 
that  the  plans  for  defence  by  sea  mines  should  be  drawn  up  by  an 
adept  well  versed  in  harbour  defence  generally  aiid  submarine  mining 
in  particular.  The  artillery  defence  must  be  carefully  noted,  as  well 
as  the  numerous  local  peculiarities  of  tidal  current,  depth  of  water, 
facilities  for  navigation,  and  other  matters  of  this  nature. 

The  object  of  any  attack  must  always  be  kept  in  view  when  designing 
the  mine  defences,  which  should  confoiiu  with  tlie  requirements  of  each 
situation. 


187 


CHAPTER    XVI. 

Boat  and  Steamer  Equipment. 

As  regards  the  boats  and  steamers  required  for  laying  or  raising 
the  mines  at  any  station,  the  establishment  will  vary  according  to  the 
number  of  mines  to  be  laid,  the  distances  of  the  mine  fields  from  the 
store  depots,  and  other  considerations.  At  some  harbours  a  small 
mooring  steamer,  say  45  ft.  long,  a  junction  box  boat,  and  a  few  cutters 
and  12  ft.  dinghies,  are  sufficient.  At  a  large  and  important  harbour 
where  rough  water  may  often  be  met  with,  larger  mooring  steamers  are 
required,  and  an  increased  number  of  boats.  Also,  if  the  mine  fields 
are  distant  from  the  depots,  one  or  more  store  vessels  or  lighters  and  a 
steam  tug  should  be  provided. 

The  Boats  should  all  be  strongly  built,  and  should  be  fitted  with 
smooth  iron  fair  leads  on  the  bow  and  stern,  through  which  ropes  can 
be  led  without  chafing.  Metal  rowlocks  that  turn  inboard  when  required 
to  be  out  of  the  way  of  ropes,  should  also  be  used. 

Junction  Box  Boats,  or  boats  specially  adapted  for  work  connected 
with  the  junction  boxes,  should  possess  a  bow  joggle  and  small  fore 
deck ;  and  as  it  is  desirable  that  the  electrical  connections  should  be 
made  under  shelter  from  rain  or  spray,  the  central  well  of  the  boat 
should  be  covered  with  canvas  on  a  suitable  framework. 

A  small  hand  crab  is  often  useful.  Although  these  junction  box 
boats  are  generally  towed  into  position  and  home  again,  it  may  some- 
times be  necessary  for  the  crew  to  shift  the  position  of  the  boat  by 
rowing.  Oars  with  rowlocks  that  turn  inboard  should  therefore  be 
provided. 

The  Steam  Tugs  may  be  any  ordinary  harbour  steamer  of  moderate 
size  used  for  this  purpose.  The  small  tugs  on  the  Thames,  Mersey,  and 
Southampton  water,  would  answer  admirably — indeed  some  of  them 
could  with  but  little  expense  be  fitted  with  special  applicances  and  then 
act  as  mooring  steamers. 

The  Store  Lighters  should  be  about  50  ft.  by  15  ft.,  4ft.  draught  and 
3  ft.  freeboard.  They  should  be  fitted  with  two  steam  or  hand  crabs 
with  quick  and  slow  speed,  and  two  iron  derricks  liaving  a  sweep  of 


188  Submarine  Mining. 

about  15  ft.  These  derricks  can  be  slewed  by  worm  gearing  driven  \>y 
hand. 

The  liglitors  should  possess  ample  room  in  the  hold,  and  the  central 
hatch  should  be  under  the  sweep  of  the  derricks,  which  may  therefore 
be  placed  about  27  ft.  apart. 

The  Small  Mooring  Steamers  may  be  45  ft.  long,  10  ft.  beam,  3  ft. 
6  in.  draught,  and  4  ft.  freeboard  at  bow.  Such  a  vessel  specially  fitted 
for  mooring  sea  mines  has  been  designed  by  the  writer  and  worked  out 
in  detail  at  Messrs.  Day,  Summers,  and  Co.,  of  Southampton.  She  is 
light  enough  to  be  sent  to  any  part  of  the  world  as  deck  freight  in  a 
large  vessel,  the  boiler  and  machinery  going  separately.  She  is  provided 
with  a  combination  of  derrick  and  winch,  which  has  recently  been 
patented.  The  derrick  has  a  straight  hollow  mast  of  steel  carrying  a 
pulley  at  the  top  and  another  at  the  jib  end  for  a  wire  rope  with  ball 
weight  and  hook.  The  mast  pivots  on  a  box  fixed  to  the  floor  of  hull, 
and  the  wire  rope  passes  through  the  pivot  centrally  to  a  pulley  secured 
to  the  hull,  and  thence  to  another  under  the  winch  which  is  conveniently 
fixed  to  the  deck  further  aft.  This  is  provided  with  two  outside  warping 
barrels  driven  preferably  by  steam  on  a  secondary  shafting,  and  a 
central  drum  driven  independently  by  a  worm  and  hand  gear  actuates 
the  wire  rope  to  derrick.  The  warping  drums  are  employed  for  raising 
the  mines,  anchors,  <tc.,  to  the  surface,  and  the  derrick  for  slinging 
them  or  bringing  them  inboard,  after  they  come  to  the  surface.  The 
derrick  mast  passes  through  a  strong  collar  secured  to  the  deck,  and 
immediately  under  this  is  keyed  a  wheel  moved  by  a  worm  on  a  shaft 
leading  to  a  position  abaft  the  winch,  where  it  is  driven  by  a  large 
handwheel  that  projects  for  neai'ly  half  its  diameter  thi'ough  the  deck. 
The  difficulty  encountered  with  the  derricks  hitherto  employed,  viz., 
that  the  weight  on  jib  end  had  to  be  slightly  raised  when  the  derrick  is 
slewed,  and  which  has  caused  the  proposed  adoption  of  steam  slewing  gear 
in  the  British  service,  is  thus  obviated.  Moreover,  as  the  weights  taken 
on  the  derrick  are  only  raised  for  a  few  feet  the  combined  winch  meets 
the  requirements  in  the  simplest  possible  manner  (see  Figs.  88  and  89). 

This  small  steamer  is  completely  decked  in  (thus  giving  sleeping 
accommodation  for  the  crew  both  in  the  fore  and  aft  cabin),  and  the 
engine  and  boiler  compartments  are  covered  with  suitable  skylights. 
Good  deck  space  is  provided  both  at  bow  and  stern,  also  the  usual  bow 
joggle,  fair  lead  over  stern,  iron  cleats  and  bulwarks,  ikc.  She  has  three 
water-tight  bulkheads,  one  in  front  of  the  derrick  (a  collision  bulkhead), 
another  in  front  of  the  boiler,  and  the  third  abaft  the  engines.  Tlie 
steering  wheel  is  placed  just  abaft  the  latter  bulkhead,  and  care  is 
taken  to  give  good  turning  power,  viz.,  a  circle  of  less  than  two  lengths 


Moorivg  Steamers. 


189 


dianu'ter.  The  engines,  eonipound,  non-condensing,  ))ut  exhausting 
tlirough  a  tank  to  heat  the  feed,  drive  a  single  screw  propeller—  a  spetid 
of  about  nine  knots  being  obtained. 

A  Larger  Steamer,  75  ft.  long,  15  ft.  beam,  4  ft.  6  in.  draught,  and 
5  ft.  6  in.  freeboard  forward,  with  similar  general  arrangements,  but 
with  higher  speed ;  a  steering  bridge,  a  small  chart-room  on  deck,  and 
altogether  a  more  powerful  boat  and  suited  for  rougher  water,  has  also 
been  designed  in  detail. 

A  second  derrick  can  be  placed  on  this  steamer  abaft  the  engine-room 
if  desired,  this  being  done  now  in  our  service ;  but,  inasmuch  as  mines 
are  slung  to  the  sides  of  a  mooring  steamer  by  the  cranes  at  a  pier-head, 
or  by  the  derricks  of  a  store  lighter,  the  necessity  of  such  an  addition  is 
not  evident.  All  mines  and  anchors  should  certainly  be  raised  to  the 
bow  joggle. 


STEAM  SCfffvr  M 


Such  a  steamer  when  fitted  with  sails  can  be  sent  to  any  part  of  the 
world.  A  vessel  of  this  description  would  be  a  useful  auxiliary  in  the 
active  defence  of  a  harbour  after  the  mines  are  laid,  and  with  this 
object  in  view  fittings  should  be  provided  for  mounting  a  Hotchkiss 
quick-firing  gun,  and  an  electric  light — say  a  60  centimetre  Mangin 
lantern  with  inclined  hand  lamp.  The  dynamo  and  its  engine  could 
be  fixed  in  the  engine-room  and  be  driven  by  the  engineer  for  the  pro- 
pelling machinery.  The  master  and  deck  hands  of  the  steamers,  and 
the  crews  of  the  smaller  boats,  should  be  well  acquainted  with  the  local 
peculiarities  of  the  harbour  in  which  the  work  is  carried  out,  and  they 
should  be  changed  as  seldom  as  circumstances  permit. 


190 


CHAPTER  XVII. 
Practical    Work. 

Surveying  the  Mine  Fields. — Some  harbours  have  been  carefully 
surveyed  at  recent  date,  and  large  scale  charts  exist  showing  the 
soundings  with  sufficient  exactitude  for  sea  mining  ;  but  many  harbours 
have  not  been  recently  surveyed,  and  it  is  then  necessary  to  check  the 
depths  of  water  at  the  positions  of  the  electro-contact  mines,  and  of 
mines  fitted  with  circuit-closers,  and  of  mechanical  mines. 

When  the  shore  is  not  very  distant,  alignment  posts  can  be  set  up 
showing  the  direction  of  each  row  of  mines,  or  of  junction  boxes,  and 
the  angle  therewith  formed  by  a  line  joining  one  of  the  mine  field  points 
with  a  distant  object  being  known  by  plotting  same  on  the  mine  field 
chart,  a  boat  can  be  placed  in  exact  position  by  means  of  a  sextant  in 
the  boat,  or  by  means  of  a  theodolite  at  the  distant  object  on  shore.  A 
sounding  can  then  be  taken,  and  the  time  of  doing  so  recorded. 
A  tide  gauge  should  be  fixed  at  the  pier-head,  or  otherwise,  and  readings 
taken  every  five  minutes.  The  sounding  can  then  be  subsequently 
corrected  for  tidal  level,  and  be  bi-ought  to  a  common  datum,  generally 
mean  low-water  mark,  spring  tides.  When  the  water  is  deep  the 
soundings  must  be  taken  at  slack  tide,  and  a  heavy  lead,  15  lb.  or  20  lb., 
be  employed. 

An  experienced  hand  is  required,  or  somewhat  startling  inaccuracies 
will  be  recorded  and  vouched  for  as  absolutely  correct.  It  lias  been 
suggested  to  employ  instruments  that  automatically  record  the  depth 
by  ineans  of  water  jJressure  indicators. 

Sir  William  Thomson's  aj^paratus  arranged  for  depths  up  to  30  fathoms 
might  be  useful.  Another  instrument  of  a  similar  nature,  but  which 
at  once  records  the  depth  by  means  of  an  electrical  tell-tale  on  board, 
is  now  in  the  market.  When  using  instruments  of  this  description,  it 
is  not  necessary  to  work  during  slack  tide,  and  much  time  can  there- 
fore be  saved  by  their  use.  In  whatever  way  the  soundings  are  taken, 
no  trouble  should  be  spared  in  order  to  insure  accuracy,  and  thus  avoid 
subsequent  annoyance.  Few  things  are  more  exasperating  than  to  see 
a  gi'oup  of  contact   u)ines  bobbing  about  on  the  surface  at  low    water 


Laying  Mines  and  Cables.  191 

slack  when  it  was  intended  to  give  them,  say,  2  fathoms  submersion  at 
that  time.  Such  a  group  would  require  to  be  raised  and  the  error 
rectified  when  every  one  would  be  working  at  high  pressure  to  get  other 
groups  down  as  quickly  as  possible.  Having  made  a  careful  survey  of 
each  mine  field,  the  length  of  the  mooring  lines  can  be  corrected  if  any 
alterations  in  the  soundings  have  occurred  since  the  last  survey.  Check 
soundings  should  be  taken  annually  to  discover  whether  the  depth  at 
different  places  remained  constant.  This  is  especially  necessary  in  the 
channels  of  a  river  and  the  entrance  of  harbours  where  the  scour  is 
considerable.  At  the  mouths  of  some  harbours  sand  banks  are  thrown 
up  in  a  single  night  by  strong  gales. 

Preparations  for  Laying  Mines. — When  it  appears  likely  that  the 
mines  may  have  to  be  laid,  the  working  parties  should  be  organised  in 
accordance  with  a  previously  prepared  programme  of  operations,  showing 
each  day's  and  each  night's  work. 

All  machinery  should  be  tried,  coal  and  other  stores  issued,  and  every 
preparation  made  to  start  the  work  rapidly  and  systematically  at  a 
moment's  notice. 

Authority  in  the  Queen's  name  should  be  obtained  to  prohibit  fisher- 
men and  others  from  dredging  and  netting  in  certain  waters,  and  to 
impose  heavy  penalties  for  disobedience.  The  friendly  channels  to  be 
preserved  through  the  waters  to  be  mined  should  be  buoyed,  and  a 
number  of  buoys  that  mean  nothing  should  be  laid  to  perplex  a  stranger 
and  draw  his  attention  from  those  which  are  important.  Instructions 
should  be  issued  to  the  men  on  the  advanced  lightships,  if  any,  to  ex- 
tinguish the  light  in  certain  contingencies.  Men  told  oil'  to  act  as 
watchers  should  be  sent  to  these  vessels  as  they  would  be  required  for 
piloting  and  other  purposes,  such  as  cautioning  vessels  concerning  any 
changes  in  the  harbour  navigation. 

Layiwj  the  Cables  and  Mines. — Assuming  that  all  the  stores  have 
been  prepared,  the  first  work  to  be  done  on  receiving  the  order  to  lay 
the  mines  is  to  lay  the  trunk  cables  and  to  connect  up  the  mines. 
These  operations  may  usually  be  conducted  simultaneously,  and  as  soon 
as  the  first  few  groups  are  ready,  they  can  be  taken  to  the  pier-head  and 
slung  to  the  mooring  steamers,  or  placed  on  board  the  store  lighters. 

The  more  important  mines,  tactically,  should  be  laid  first,  the 
advanced  positions  being  of  chief  value  in  some  harbours,  the  retired 
positions  in  others.  If  the  tactical  values  of  the  various  mine  fields  do 
not  diSer  greatly,  those  in  advance  should  be  first  attended  to,  for 
obvious  reasons. 

Laying  the  Trunk  Cables. — As  stated  in  a  previous  chapter,  some  of 
the  main  cables  may  often  be  laid  permanently,  and  their  ends  buoyed. 


192  Submarine  Mining. 

It  would  not,  however,  be  prudent  to  allow  their  positions  to  be  known, 
and  the  buoys  should  therefore  be  treated  like  dormant  mines  (see 
Fig.  36,  page  73).  The  explosive  link  may  be  arranged  to  hold  down  a 
small  buoy  attached  to  a  line,  and  this  to  a  chain  by  which  the  cable 
end  and  a  small  sinker  can  be  raised  to  the  surface  whenever  required. 
A  heavy  sinker  should  be  attached  to  the  cable  at  such  a  distance  from 
its  extremity  that  when  the  cable  end  is  brought  to  the  surface  this 
sinker  remains  unmoved,  and  forms  an  anchor  to  which  the  boat 
employed  in  the  operation  can  ride.  A  junction  box  may  be  added 
to  the  cable  end  as  soon  as  the  mines  are  ready  to  be  laid. 

Cables  can  be  laid  from  an  iron  drum  provided  with  a  friction  l)rake, 
or  from  a  coil  made  on  the  deck  of  a  steamer  or  lighter,  or  from  the 
special  barge  already  described  on  page  165.  In  laying  from  coils  care 
must  be  taken  to  protect  the  men  employed  when  clearing  same,  and 
it  is  always  advisable  to  rig  up  some  kind  of  brake  to  check  the  cable, 
especially  when  laying  it  in  deep  water.  If  the  mine  field  be  some 
distance  from  the  shore,  it  is  necessary  to  lay  to  the  shore,  and  then 
land  the  shore  end ;  but  when  the  mines  are  near  to  the  firing  station 
the  main  cables  can  be  laid  from  the  shore  outwards,  the  shore  end 
being  previously  landed  and  connected  electrically  with  the  firing  station 
by  cables  laid  in  deep  trenches.  "When  no  main  cables  are  used  the 
cable  from  each  mine  is  of  course  laid  with  the  mine,  and  the  shore 
end  landed  last. 

Special  shore  end  cables,  with  heavy  armouring,  which  are  used  in 
exposed  positions,  should  be  laid  permanently,  and  the  other  cables  are 
then  connected  to  the  outer  ends,  thus  avoiding  landing  operations 
when  the  mines  have  to  be  laid,  and  saving  a  good  deal  of  time,  even  in 
fine  weather. 

Connecting  up  the  Mines. — The  operation  of  connecting  up  the  mines 
with  their  cables,  tripping  chains,  ifec,  can  generally  be  performed  in 
the  open  air  on  the  connecting-up  ground,  but  in  wet  weather  it  is 
desirable  to  do  it  under  cover  if  a  suitable  shed  be  available.  If  not, 
movable  jointing  hoods  should  be  used,  as  in  the  street  work  of  the 
postal  telegraphs.  The  depot  tramway  should  be  led  to  the  connecting- 
up  ground,  so  that  the  mines  may  remain  on  tlie  trucks  from  the  time 
they  leave  the  magazine  until  they  are  embarked. 

The  mines,  loaded  and  fitted  with  their  firing  and  other  apparatus, 
having  arrived  on  their  trucks  at  the  connecting-up  ground,  or  shed,  the 
crowned  cable  ends  are  fixed  to  the  mouths  of  the  mines  by  screw  clamps, 
and  the  electric  joint  or  joints  carefully  made.  The  tripping  chains  are 
then  secured  and  stoppered  to  the  cable  with  spun  yarn,  so  that  the 
cables  are  slack  when  a  strain  comes  on  the  chains. 


Connecting,  EmharJdng,  and  Laying  Mines.  193 

With  buoyant  mines  the  mooring  lines  are  attached  to  the  slings  or 
attachment  chains,  but  the  sinkers  can  be  connected  to  the  tripping 
chains  and  mooring  lines  after  the  mines  are  slung  on  the  side  of  the 
mooring  steamer.  A  sinker  can  be  put  on  each  truck  carrying  a  buoyant 
mine  on  its  way  to  the  pier-head. 

There  should  be  four  or  five  trained  men  in  each  working  party,  and 
one  to  direct.  With  a  little  practice  the  men  can  be  taught  to  connect 
up  the  different  types  of  mines  and  the  different  arrangements  with 
celerity,  the  men  falling  naturally  into  their  places  and  performing 
each  operation  as  required.  In  our  service  a  party  is  told  off  by  num- 
bers, and  each  man's  duties  are  detailed,  but  a  hard-and-fast  method  of 
procedure  for  work  of  this  character  is  not  desirable,  and  causes  a  loss, 
rather  than  a  gain  of  time.  It  is  similar  to  riggers'  work,  and  the 
method  of  procedure  should  be  elastic  rather  than  arbitrary.  Hand 
sketches,  with  figured  dimensions  at  length,  are  useful,  and  the  officer 
in  charge  should  supply  them  to  the  directors  of  the  working  parties 
whenever  practicable. 

Embarking  and  Laying  Alines. — Electro-contact  mines,  in  groups,  on 
the  fork  system,  can  be  embarked  and  laid  singly  if  a  store  lighter  be 
close  at  hand,  but  the  mines  for  an  entire  group  are  generally  slung  to 
the  mooring  steamer,  one  mine  with  its  sinker  at  the  bow,  the  others 
with  their  sinkers  on  the  sides  of  the  steamer,  and  the  branch  cables 
arranged  in  coils  on  the  deck  ready  and  suitably  for  paying  out.  The 
slinging  can  be  done  by  the  crane  at  the  pier-head,  or  by  the  derricks 
on  the  store  lighter.  Each  sinker  can  be  slung  by  a  greased  lowering 
line  of  sufficient  strength,  and  of  a  minimum  length  of  rather  more  than 
twice  the  depth  of  water  where  the  mine  is  to  be  moored.  Each  mine 
is  slung  by  a  shorter  lowering  line.  The  mooring  line  is  then  shackled 
to  the  centre  lug  of  the  sinker,  and  the  tripping  chain  to  one  of  the  side 
lugs.  The  mooring  line  and  cable  between  the  sinker  and  the  mine 
are  then  coiled  and  tied  to  the  side  of  the  steamer  with  a  piece  of  spun 
yarn  that  will  break  when  a  strain  comes  upon  it. 

Laying  the  Mines. — The  vessel  now  steams  close  to  the  position  of 
the  first  mine  to  be  laid,  which  is  found  by  alignment  posts  on  shore,  or 
by  the  sextant,  or  by  both  combined.  The  steamer  is  slowed  and 
brought  bow  on  to  the  current  (if  any),  and  the  sinker  is  lowered 
away  by  word  of  command  until  the  weight  comes  on  the  mine.  The 
lowering  line  of  the  sinker  is  hauled  in,  and  when  the  exact  position  of 
the  mine  is  covered,  the  mine  is  lowered  away  also. 

Another  method  which  is  more  easily  performed,  but  less  accurate,  is 
to  sling  both  mine  and  sinker  with  short  lines,  and  release  them  suddenly 
and  simultaneously  when  the  mine  position  is  covered — care  being  taken 
that  no  sudden  strain  is  thus  thrown  on  the  branch  cable. 
o 


194  Subinarine  Mining. 

Whichever  plan  be  pursued,  the  cable  is  taken  aft  and  paid  over  the 
stern  as  soon  as  the  vessel  gathers  way,  and  proceeds  slowly  to  the  group 
junction  box,  when  a  throw  line  is  attached  to  the  end  of  the  cable,  and 
it  is  transferred  to  the  party  in  the  junction-box  boat,  who  proceed  to 
make  the  necessary  electric  connections. 

The  other  mines  of  the  group  are  then  laid  in  the  same  way.  When 
a  small  steamer  is  used  the  mines  should  be  slung  so  that  they  can  be 
laid  alternately  from  the  port  and  starboard  side,  thus  keeping  the 
vessel  in  trim  as  far  as  possible. 

When  electro-contact  mines  are  connected  up  in  a  string,  see  Fig.  60, 
page  125,  their  cables  branching  from  the  single  main  cable  at  a  series 
of  single  connecting  boxes,  each  fitted  witli  a  single  disconnector,  see 
Fig.  50,  page  106,  they  are  slung  to  the  bow  and  sides  of  a  steamer  in 
a  somewhat  similar  manner,  but  they  are  laid  one  after  the  other  in 
one  continuous  operation,  each  being  lowered  as  soon  as  the  cable 
between  it  and  the  last  mine  laid  becomes  taut.  The  group  being  laid, 
the  single  main  cable  is  paid  out  and  carried  either  to  a  multiple  main 
junction  box  (where  it  is  connected  to  one  of  the  cores),  or  to  the  firing 
station  on  shore.  If  a  75  ft.  steamer  be  employed,  an  entire  group  may 
be  slung  on  one  side  of  the  vessel,  but  with  smaller  steamers  the  mines 
should  be  slung  and  laid  from  opposite  sides  of  the  vessel  in  alternate 
pairs,  in  which  event  the  cable  must  be  passed  under  the  mooring 
steamer  from  one  side  to  the  other  when  necessary. 

Embarkiyig  and  Laying  Mines  to  he  Fired  by  Observation. — These 
mines  can  be  slung  to  the  bow  and  sides  of  the  mooring  steamer  in  a 
similar  manner  to  electro-contact  mines  arranged  on  fork,  as  already 
described.  When  each  mine  is  lowered  a  man  should  be  told  off  to 
stand  close  to  the  lowering  line  and  lower  a  flag  or  make  other  visual 
signal.  Observers  on  shore  should  at  the  same  moment  bring  the 
coUimation  of  the  observing  instruments  on  the  position  of  tiie  flag, 
clamp  them  when  the  flag  is  lowered,  and  keep  a  record  of  the  angles  as 
shown  by  the  instruments. 

Mine  Field  Repairs. — When  the  electric  testing  shows  tliat  a  group 
of  electro-contact  mines  is  out  of  order,  a  suitable  boat  should  be  sent 
to  the  group  box,  the  buoy,  if  dormant,  being  first  brought  to  the  surface 
by  tiring  the  explosive  link.  (If  the  buoy  will  not  rise  the  defect 
probably  exists  between  shore  and  box,  and  the  cable  must  be  underrun 
by  a  steamer.)  Should  the  main  cable  be  in  good  order,  the  box  is 
raised,  and  each  mine  tested  singly,  tlie  faulty  mine  or  branch  being 
thereby  discovered.  The  branch  cable  being  disconnected  from  the  box, 
is  then  transferred  to  a  mooring  steamer  by  means  of  a  throw  line,  and 
th(!  braiicli  cable  is  underrun  and  carefully  examined  as  it  comes 
inboard.     As  soon  as  the  tripping  chain  comes  to  the  surface  it  is  taken 


Mine  Field  Repairs.  195 

to  tlie  bow  joggle  of  the  steamer  and  carried  to  the  warping  drum  of 
the  winch  or  capstan — preferably  driven  by  steam.  The  sinker  is  then 
raised,  the  mine  secured  as  soon  as  it  comes  to  the  surface,  and  the 
fault  discovered  at  once  if  possible.  Failing  this,  the  mine  is  taken  to 
the  store  ship  or  to  the  depot,  where  it  is  disconnected  and  the  fault 
localised.  If  the  necessary  repair  can  be  quickly  rectified  the  mine  is 
relaid,  but  it  generally  saves  time  to  have  ;i  small  reserve  of  loaded 
mines  ready,  and  to  connect  up  one  of  these  and  lay  it  at  once. 

When  the  electric  tests  show  that  an  observation  mine  is  out  of  order, 
a  suitable  boat  should  be  sent  to  the  multiple  main  junction  box  to  raise 
it.  The  mine  cable  is  then  transferred  to  a  mooring  steamer,  which 
should  underrun  the  cable  and  raise  the  mine,  the  entire  operation 
being  very  similar  to  the  one  just  described. 

Should  a  group  of  electro-contact  mines  moored  in  series  get  out  of 
order,  its  i-epair  is  a  serious  matter,  as  the  whole  of  the  group  must  be 
raised,  even  if  the  fault  be  discovered  in  the  first  mine.  The  mines  are 
nearly  certain  to  be  dragged  out  of  position  directly  the  steamer  raises 
the  iirst  mine.  It  may,  therefore,  sometimes  be  preferable  to  try  the 
curative  effect  frequently  obtainable  by  applying  the  firing  current, 
already  alluded  to  in  a  previous  chapter. 

Mines  are  moored  in  so  many  different  manners — some  with  and 
others  without  detached  circuit-closers,  some  on  single  and  others  on 
double  moorings,  some  on  the  bottom  and  others  buoyant — that  it 
would  weary  the  reader  if  the  laying  and  raising  of  each  were  given 
in  detail. 


o2 


196 


CHAPTER  XVIII. 
The  Personnel  and  the  Stores. 

The  organization  and  superintendence  and  designing  required  for 
submarine  mining  are  performed  in  our  ser\dce  by  the  officers  of  the 
Royal  Engineers,  who  are  frequently  expert  boatmen,  and  who,  from 
their  high  educational  attainments,  are  easily  trained  in  the  scientific 
portions  of  the  work.  It  is  rather  hard  upon  them,  for  experience  shows 
that  it  practically  destroys  their  chance  of  seeing  active  service  in  the 
field.  As  for  the  men  it  is  impossible  to  give  any  sound  reasons  for 
employing  our  most  expensive  and,  under  many  conditions,  our  most 
useful  soldiery  in  this  manner.  Our  small  force  of  Royal  Engineers 
would  1)6  urgently  required  at  the  front  in  the  event  of  a  war  of  such 
magnitude  that  our  harbours  would  have  to  be  mined.  The  same 
argument  applies  with  equal  or  greater  weight  to  our  Navy,  and  to  a 
less  extent  to  any  other  portions  of  our  fighting  forces. 

For  this  reason,  if  for  no  other,  it  is  important  that  civilians  should 
perform  all  the  services  possible  which  are  connected  with  harbour 
defences.  Submarine  mining  is  certainly  one  of  them.  An  attempt  is 
being  made  at  some  ports  to  employ  the  Volunteers  as  miners,  and 
no  pains  should  be  spared  to  insure  success  if  possible,  but  the 
results  to  date  are  not  encouraging.  It  is  not  a  popular  service  with 
them.  It  is  rather  cold,  wet,  and  dirty  work  with  very  little  soldier- 
ing about  it.  Much  of  it  is  very  like  oyster  dredging  with  more 
tallow,  tar,  and  twine.  Only  a  small  proportion  of  the  men  are 
required  for  the  scientific  arrangements  connected  with  the  electrical 
gear.  After  an  experience  extending  over  a  number  of  years  I  am 
convinced  that  most  of  the  work  can  be  properly  and  economically 
performed  by  civilians  under  the  superintendence  of  trained  officers. 
At  Singapore  and  Hong-Kong,  Malays  and  Chinese  boatmen,  who  can- 
not speak  the  English  language,  and  who  are  only  instructed  for  short 
periods  annually,  have  been  employed  with  satisfactory  results;  the 
work  being  directed  by  a  small  nucleus  composed  of  highly-trained 
regulars.      INluch  more  tlicn  should    civilians  and  volunlocrs  at  liome  be 


Civilfan  Personnel  Recommended.  197 

able  to  act  in  a  similar  manner,  but  the  nucleus  should  l)o  composed  of 
men  permanently  employed  at  each  port. 

Intelligent  men  of  experience  in  boat  or  steamer  work,  soon  learn 
how  to  proceed.  To  fill  a  drill-book  with  directions  that  No.  1  shall  do 
this,  No.  2  that,  and  so  forth,  savours  of  military  pedantry.  The 
civilians  employed  by  the  dockyards  or  by  the  Trinity  Board  in  laying 
and  raising  channel  buoys  are  not  drilled  by  numbers,  and  in  practical  sea 
mining  the  drills  are  seldom  if  ever  followed.  Indeed,  it  is  not  possible, 
because  the  circumstances  vary  so  frequently.  As  a  rule,  one  or  two 
good  men  in  each  squad  do  most  of  the  work,  and  the  rest  assist  when 
required.  No  doubt  it  is  difficult  to  convert  soldiers  into  sailors  ;  but 
the  drill-book  assists  in  the  process  no  more  than  the  guernseys  and 
men-o'-war  caps  that  are  donned. 

Whenever  possible  the  men  employed  for  the  water  work  connected 
with  submarine  mining  should  be  able-bodied  seamen,  who  should  sign 
articles  and  be  under  the  discipline  of  the  masters  of  the  mooring 
steamers,  who  themselves  are  under  the  orders  and  guidance  of  the 
superintending  officers. 

The  rough  work  on  shore,  such  as  coiling  cables,  moving  weights,  &c.. 
can  be  done  by  labourers,  and  the  electrical  work  can  be  done  by  per- 
manent hands  who  have  received  a  special  training,  whether  it  be  in  or 
out  of  the  service.  There  is  not  the  slightest  necessity  for  a  single 
scarlet  jacket  or  pipe-clayed  belt.  The  men  should  be  clad  as  boatmen. 
They  should  not  be  moved  en  bloc  from  one  station  to  another  at  the 
beck  and  call  of  the  adjutant-general.  They  should  be  or  become 
acquainted  with  the  local  peculiarities  of  the  waters  of  their  port.  The 
working  parties  and  the  programme  of  operations  for  the  day  should  not 
be  upset  by  unforeseen  regimental  troubles.  If  men  misbehave  them- 
selves as  civilians  they  can  be  discharged.  A  number  of  men  would 
not  daily  be  required  for  all  kinds  of  regimental  and  garrison  duties. 
In  short  the  work  during  peace  would  be  done,  where  it  is  now  done  at 
all,  with  a  considerable  reduction  in  the  numbers  of  the  personnel,  and 
a  still  greater  savdng  in  £  s.  d.  The  idea  that  Sapper  labour  is  cheaper 
than  civilian  labour  is  entirely  fallacious.  In  a  paper  read  at  the 
Royal  United  Service  Institution  on  March  18,  1887,  I  showed  that  the 
cost  of  a  high-class  civilian  crew  in  a  large  mooring  steamer  came  to  5d. 
per  working  hour  per  man,  and  that  the  cost  per  working  hour  per  man 
of  a  submarine  mining  company  of  Royal  Engineers  was  Is.  Good 
labourers  can  be  hired  for  3d.  in  the  winter  and  4d.  in  the  summer  for 
temporary  employment,  and  expert  boatmen  for  6d.  an  hour.  But 
efficiency  is  of  more  importance  than  cost,  and  if  it  could  be  shown  that 
the  service  is  better   performed  by  Sappers  than  it  can  be  by  civilians 


198  Suhviarine  Mining. 

no  one  would  desire  a  change  if  the  Sappers  were  not  wahted  in 
war  for  other  duties.  But  this  cannot  be  shown.  The  companies 
are  frequently  moved,  the  men  transferred  before  they  learn  local  pecu- 
liarities, and  the  works  are  interfered  with  by  regimental  necessities. 

Those  who  advocate  soldiers  for  sea  mining  fear  that  civilians  would 
desert  when  war  came  upon  us.  If  so,  they  must  also  anticipate  the 
desertion  of  the  personnel  from  Her  Majesty's  dockyards,  as  these  men 
are  as  likely  to  be  "  under  fire  "  as  the  submarine  miners.  Higher  pay 
would  be  expected  and  probably  be  given,  but  no  man  worth  retaining 
would  desert  at  such  a  time.  The  personnel  for  an  ordinary  station 
might  be  somewhat  as  follows  :  Two  or  three  highly  trained  officers 
for  directing ;  one  mooring  steamer  with  civilian  crew ;  one  mooring 
party,  six  civilians,  under  a  good  leading  hand  ;  one  depot  party  ditto ; 
one  stoi'ekeeper.  Engine  drivers  and  electricians,  according  to  require- 
ments, to  keep  the  machinery  and  electrical  equipment  in  good  order. 
Artisans,  labourers,  and  boatmen  hired  as  required.  Also  one  small 
company  of  volunteers  under  local  officers  who  are  professionally  con- 
nected with  work  of  a  similar  nature  ;  the  employers  of  labour  in  small 
shipyards,  for  instance.  Such  a  company  should  be  recruited  from  the 
local  boatmen,  shipwrights,  and  artisans.  Men  should  be  encouraged 
to  join,  not  boys.  Directly  war  appeared  to  be  imminent,  additional 
civilian  electricians,  engine  drivers,  and  lajbourers  would  be  secured. 
Much  difficulty  will  always  be  met  with  in  finding  time  and  opportunity 
to  train  each  volunteer  in  the  multifarious  duties  of  a  submarine 
miner.  It  is  therefore  desirable  to  divide  the  work  as  far  as  possible, 
and  teach  the  men  in  squads  to  do  a  few  things  well,  rather  than  the 
whole  indifferently.  If  experience  should  prove  that  the  volunteer 
movement  is  not  applicable  to  this  class  of  work,  an  honest  attempt 
should  be  made  at  some  of  the  stations  to  work  with  a  permanent  estab- 
lishment of  civilians,  and  a  comparison  could  then  be  made  between  the 
relative  cost  and  efficiency  of  this  and  the  present  military  organizations. 

The  Royal  Engineer  and  auxiliary  forces  now  employed  are  quite 
insufficient,  and  the  danger  caused  by  this  deficiency  is  increased  by  the 
extreme  and  totally  unnecessary  complexity  of  our  service  arrangements, 
which  entail  a  long  and  careful  training  of  the  personnel  in  order  to 
insure  success. 

This  training  should  in  any  case  be  simplified  as  much  as  possilile  by 
teaching  the  men  certain  duties  and  keeping  them  to  these  duties, 
instead  of  making  them  so  many  jacks-of -all-trades  and  masters  of  none. 
If  a  man  is  to  drive  an  engine  when  war  is  declared,  why  teach  him 
(Oectricity  1  If  another  is  to  operate  an  electric  light,  why  teach  him 
submarine  mining?    The  ofiiccrs  alone  need  to  know  it  all   thoroughly. 


Brifhh  Syf^tem.  Criticized  199 

As  to  the  rest,  there  should  be  division  of  labour  and  division  of 
instruction.  With  a  military  system  it  is  very  difficult  to  do  this. 
Tom  goes  on  guard  and  John  must  take  his  place  on  the  works,  or  the 
works  must  stop.  Each  must  know  a  little  about  a  great  deal.  It  is  far 
better  for  them  to  know  a  great  deal  about  a  little.  With  civilians  on 
the  works  this  idea  can  be  followed  out.  But  whatever  may  be  the 
personnel,  and  whatever  the  system  of  firing  and  testing  the  mines 
which  is  adopted  by  any  country,  they  should  be  such  that  the  mines 
can  be  very  quickly  laid  after  the  order  to  do  so  has  been  received.  If 
our  present  system  and  personnel  be  considered  satisfactory,  let  the 
adjutant-general  suddenly  and  unexpectedly  give  an  order  that  the 
mines  shall  be  laid  forthwith  in  all  our  harbours  which  are  assumed  to 
be  prepared  for  such  an  event,  and  let  him  countermand  the  order  at 
the  end  of  a  fortnight  and  ask  for  reports  from  all  these  stations  showing 
the  progress  of  the  work  at  that  time,  the  number  of  mines  laid  and  in 
working  order  with  their  firing  stations  and  operators,  the  number  of 
test  rooms  fitted  and  provided  with  the  necessary  trained  testers,  the 
number  of  electric  lights  efficient,  <fec.  The  results  would  perhaps  open 
the  eyes  of  the  authorities  to  the  fact  that  seci'ecy  in  submarine  mining 
is  now  made  with  the  indefensible  object  of  hiding  our  weakness,  not 
our  strength. 

The  position  and  number  of  the  mines  only  need  be  secret.  All  the 
rest  should  be  brought  to  the  light  of  day,  and  until  this  is  done  and 
public  criticism  can  be  brought  to  bear  upon  it,  the  present  complicated 
system  and  utter  want  of  proper  means  to  work  it,  and  the  present  lack 
of  organization  will  continue.  Some  fine  day  a  great  naval  war  will 
throw  us  on  our  beam-ends,  and  the  officers  at  every  station  will  cry  out 
in  vain  for  the  highly  trained  electricians  and  personnel  generally 
which  are  required.  A  trial  at  one  station,  like  that  which  took  place 
at  Milford  Haven,  is  no  test  whatever,  because  persomiel,  stores,  and 
steamers  were  promptly  transferred  from  other  stations  to  the  scene  of 
operations.  Even  then  it  took  weeks  instead  of  days  to  get  a  section 
of  the  defences  into  working  order. 

Our  mines  contain  apparatus  requiring  a  number  of  delicate  and 
difficult  adjustments  which  are  easily  put  out  of  order  after  the  mines 
are  laid.  The  mooring  steamers  then  have  a  lively  time,  daily  repairs 
for  some  or  other  of  the  mines  being  generally  necessary. 

A  foreign  officer  told  me  recently  that  some  mines  had  been  laid  in 
his  country  for  five  years  and  are  still  in  good  order.  I  do  not 
remember  any  instance  in  which  our  mines  remained  down  for  five 
months,  only  a  portion  will  remain  in  good  order  for  as  many  weeks, 
and  some  are  unserviceable  directly  they  are  laid. 


200  Submarine  Mining. 

Our  system  is  so  intricate  that  success  cannot  possibly  be  secured 
with  any  certainty,  and  tlie  instruction  of  efficient  operators  is  most 
difficult  and  tedious. 

These  remarks  apply  not  only  to  the  mines,  but  to  the  apparatus  on 
shore,  especially  in  what  are  termed  the  test  rooms.  Here  will  be 
found  a  perfect  network  of  wires,  commingled  with  galvanometers,  tele- 
phones, commutators,  batteries,  wandering  leads,  &c.,  on  which  various 
electrical  tricks  can  be  performed.  If  all  this  delicate  apparatus  could 
keep  the  mines  in  an  efficient  state,  something  might  be  said  for  it. 
But  it  has  an  opposite  tendency,  and  although  it  is  absolutely  necessary 
to  test  mines  arranged  on  our  service  systems,  because  so  many  require 
renewal  or  repair  after  brief  periods,  it  would  nevertheless  be  infinitely 
preferable  to  employ  strong  and  simple  gear,  not  easily  deranged,  and 
therefore  requiring  but  little  if  any  testing. 

The  same  love  for  the  complex  permeates  the  larger  stores.  Steam 
machinery  is  employed  where  hand  gear  is  preferable,  as  being  less 
likely  to  break  down  at  a  critical  time,  or  to  be  damaged  by  a  chance 
shot.  For  instance,  the  mooring  steamers  contain  much  unnecessary 
machinery,  steam  cranes  are  used  on  shore  where  hand  cranes  would  be 
better,  and  so  on.  If  doubt  be  placed  on  these  opinions,  let  a  civilian 
electrical  engineer  of  high  standing  be  appointed  to  report  on  our  mine 
systems  ;  and  a  good  mechanical  engineer  on  the  hoisting  and  mooring 
and  mine  raising  arrangements.  Important  simplifications  would  soon 
be  insisted  upon,  and  the  question  as  to  the  personnel  would  then  become 
proportionally  easier  to  solve. 

The  Stores. — Let  us  now  consider  how  tlie  stores  should  be  procured. 
The  Italians  have  a  large  government  manufactory  for  submarine  mining 
stores,  and  for  some  years  these  stores  were  largely  manufactured  for 
our  service  by  the  Royal  Laboratory  at  the  Royal  Arsenal.  Experience, 
however,  proved  that  this  system  was  costly,  and  that  vexatious  delays 
frequently  occurred,  this  extra  work  being  more  or  less  shelved  when  it 
interfered  with  the  legitimate  work  of  the  manufactory.  The  require- 
ments for  submarine  mining  come  in  fits  and  starts,  and  are  not  well 
suited  for  providing  continuous  work  in  a  special  department.  It  would, 
therefore,  have  been  bad  policy  to  start  a  government  factory  for  their 
special  manufacture ;  and  there  is  no  necessity  to  do  so,  for  all  the  gear, 
except  the  instruments,  can  be  readily  made  in  good  engineering  shops. 

Moreover,  the  resources  of  the  Royal  Arsenal  would,  in  the  event  of 
war,  be  taxed  to  the  utmost,  and  the  speedy  manufacture  of  submarine 
mining  stores  could  not  then  be  relied  upon.  For  these  reasons  the 
resources  of  private  firms  have  been  utilised  in  this  country,  and  with 
considerable  success. 


The  Stores.  201 

A  few  good  tiniis  were  selected  by  the  Royal  Engineers,  and  the 
orders  were  for  some  years  placed  with  them,  often  without  competi- 
tion, when  the  prices  quoted  were  considered  to  be  fair  and  reasonable. 
In  the  year  1878  large  quantities  of  stores  were  obtained  veiy 
promptly  in  this  manner,  the  Royal  Engineei'S  directing  both  the 
purchase  and  inspection.  The  ordinary  War  Office  system  was  thrown 
to  tiie  winds,  as  it  always  must  be  in  times  of  emergency.  It  is  never 
applicable  to  scientific  stores.  The  system  of  lowest  tender  is  per- 
nicious when  applied  to  any  stores  of  the  kind.  It  is  alike  inapplicable 
to  artillery  and  to  engineer  stores,  except  perhaps  for  such  articles  as 
picks  and  shovels,  when  a  rigid  inspection  and  high  specitication  and 
pattern  may  pei'haps  protect  us  sufficiently. 

The  recent  disclosures  before  the  Committee  on  the  Sweating  System 
have  shown  that  even  with  such  articles  as  tunics,  belts,  and  saddlery, 
the  present  system  of  contracting  witli  manufacturers  at  the  lowest 
price  in  an  open  market  fails.  Much  more  then  must  it  fail  when  it  is 
necessary  to  obtain  scientific  instruments  and  stores.  The  Contract 
branch  is  perfectly  satisfied  so  long  as  the  stores  just  pass  inspection. 
It  frequently  happens  that  a  large  percentage  are  rejected  on  delivery, 
causing  a  serious  delay,  which  might  have  the  most  serious  conse- 
quences were  we  likely  to  require  them  in  a  hurry  at  an  outbreak  of 
hostilities.  The  present  system  produces  prices  which  prohibit  high- 
class  work,  and  firms  that  pride  themselves  on  never  turning  out  any 
other  kind  of  work  cannot  secure  an  order.  Shoddy  reigns  supreme, 
and  laughs  in  his  sleeve  at  an  officialdom  which  he  endeavours  to  hood- 
wink at  every  turn,  generally  with  facility,  as  instanced  by  the  two- 
ply  thread,  &c.  It  is  no  longer  an  honour,  as  it  used  to  be,  for  a  firm 
to  be  on  the  Government  list  of  contractors. 

People  absolutely  unknown  as  instrument  makers  are  asked  to  tender 
for  the  manufacture  of  confidential  instruments  that  require  the 
greatest  nicety  of  adjustment. 

Tendei\s  for  steamers  are  advertised  for  !  cfec,  &c. 

The  duties  of  the  inspecting  officers  have  become  unnecessarily  difficult 
and  arduous. 

This  system  strikes  at  the  root  of  all  good  work.  It  encourages 
middlemen,  subletting,  and  sweating.  The  middlemen  employ  indif- 
ferent workmen,  often  men  who  have  fallen  from  a  good  position,  and 
who  could  not  obtain  a  place  in  any  respectable  manufactory.  These 
men  are  ground  down  to  work  for  wages  out  of  which  it  is  almost 
impossible  for  them  to  house  and  feed  themselves.  Their  families  are 
either  starving  or  in  the  workhouse.  The  legitimate  manufacturer  has 
either  to  discharge  honest  hands  or  pay  them   such  wages  that  he  is 


202  Submarine  Mining. 

almost  ashamed  to  negotiate  with  them.  The  sweating  system  is 
gradually  permeating  the  whole  of  English  trade.  It  is  not  confined 
to  boots  and  belts.  It  is  bringing  starvation  to  the  doors  of  our 
working  millions,  to  our  political  voters.  The  present  system  of 
Government  contracts  in  all  branches  encourages  this  undesirable  state 
of  affairs. 

The  manufacture  at  the  Royal  Arsenal,  with  all  its  delay,  was  far 
better  than  this.  The  stores  were  excellent,  if  costly.  The  remedy  is 
evident.  A  return  should  be  made  to  the  system  followed  in  former 
years.  The  Government  lists  of  contivactors  should  consist  only  of 
well-known  firms  celebrated  for  honest  high-class  work,  and  the  users 
of  the  stores  should  have  a  voice  when  the  lists  are  drawn  up. 

Competition  between  firms  well  known  for  sound  work  is  sufficiently 
keen  to  keep  pi-ices  down  to  a  proper  level  for  such  work,  and  if  they 
only  competed  among  themselves,  and  had  not  to  compete  with  the 
sweater,  the  prices  would  be  such  that  a  healthy  emulation  to  produce 
the  best  article  would  be  possible. 

Stores  for  submarine  mining,  like  those  for  torpedo  gear  and  artillery, 
cannot  be  made  too  carefully.  So  much  depends  upon  each  link  of  the 
chain  between  mine  and  firing  station  being  in  good  order.  A  leaky 
rivet,  a  weak  shackle,  a  bad  electrical  connection,  or  any  one  of  a 
hundred  little  matters  of  the  kind,  may  destroy  the  efficiency  of  an 
important  mine.  Cheap  gear  is  a  mistake,  because  it  is  likely  to  fail, 
and  may  do  so  at  a  critical  moment,  when  perhaps  the  destruction  of 
an  enemy's  ironclad  is  at  stake.  Now  the  cost  of  such  a  vessel  would 
mine  twenty  or  thirty  harbours,  and  her  value  in  war  might  gi'catly 
exceed  her  cost. 


203 


CHAPTER  XIX. 
Automatic  Mines. 
ExGLAND  cannot  afford  to  put  impediments  in  the  way  of  her  own 
commerce  in  time  of  war.  Any  serious  stoppage  to  her  ocean  trade 
would  be  ahiiost  tantamount  to  defeat.  Automatic  mines  can,  there- 
fore, only  be  used  on  our  defences  to  a  limited  extent,  and  this  has 
been  recognised  from  the  first.  Foreign  nations  are  not  in  the  same 
position,  and  many  of  them  have  devoted  much  time  and  labour  in 
order  to  perfect  this  form  of  mine.  For  instance,  where  a  relatively 
weak  naval  power  has  to  quickly  block  its  rivers  and  harbours  on  the 
outbreak  of  war,  the  elaborate  electrical  arrangements  adopted  in  our 
service  could  not  be  prepared  in  time.  Moreover,  its  commerce  on  the 
Inch  seas  would  certainly  be  stopped,  and  its  harbours  be  subject  to 
partial  if  not  absolute  blockade.  Under  such  conditions  good  auto- 
matic mines  are  both  useful  and  necessary.  But  a  strong  naval  power 
would  require  them  as  a  naval  arm,  to  assist  in  blocking  the  harbours 
of  a  foe,  by  sowing  the  entrances  with  mines  of  this  nature.  Even  in 
the  harbour  and  river  defences  of  England,  there  are  some  situations 
where  automatic  mines  may  advantageously  be  laid,  the  shore  being  so 
far  off  that  controlled  mines  could  not  be  worked  satisfactorily.  It  is 
therefore  to  be  regretted  that  a  good  pattern  has  not  been  perfected  by 
one  or  other  of  our  services.  Too  little  attention  has  been  paid  to  the 
subject.  Improvised  mines  are  not  good  enough.  On  the  other  hand, 
the  mines  in  store  for  defence  purposes  contain  too  elaborate  an  appa- 
ratus, and,  in  any  event,  they  cannot  easily  be  converted  into  auto- 
matic mines  for  blockading  purposes.  No  attempt  has  been  made  to  do 
so,  and  an  Admiral  who  recently  stated  in  the  Times  that  we  are  pro- 
vided with  the  mines  for  such  operations,  must  have  been  misinformed. 

An  inherent  defect  of  most  automatic  mines  is  their  vulnerability  to 
countermining.  For  this  reason  the  cases  need  not  be  strong.  If  they 
can  resist  the  blow  of  a  countermine  wliicli  will  just  cause  the  mine  to 
explode  by  shock,  it  is  enough. 

The  chief  requirements  of  an  automatic  mine  are  that  it  should  be 
quickly,  easily,  and  safely  laid ;  also  that  it  should  be  safely  recovered 


204  Submarine  Mining. 

when  desired.  Wave  action  should  not  cause  self-destruction,  and  a 
mine  should  become  automatically  safe  if  it  break  away  from  its 
fastenings.  Moreover,  as  it  would  manifestly  be  impossible  for  vessels 
to  accurately  survey  the  waters  and  lay  the  mines  at  the  entrance  of  a 
harbour  held  by  an  active  foe,  such  mines  should  be  provided  with  an 
arrangement  for  bringing  them  automatically  to  the  required  submer- 
sion, the  mooring  line  being  unwound  until  the  proper  length  is 
obtained. 

Scores  of  inventors  have  attempted  to  produce  a  good  automatic 
mine,  but  hitherto  witiiout  complete  success.  A  few  of  tiie  different 
types  will  now  be  examined. 

Chemical  Automatic  Mines. — Professor  Jacobi's  torpedoes  were  used 
in  the  Baltic  by  the  Russians  during  the  Crimean  War.  These  mines 
were  fitted  with  a  glass  tube  containing  sulphuric  acid,  the  tube  being 
imbedded  in  a  mixture  of  chlorate  of  potasli  and  sugar.  Levers  pro- 
jected from  the  mine,  and  were  so  arranged  that  a  passing  vessel  on 
striking  one  of  them,  caused  the  glass  tube  to  be  broken  and  the  charge 
of  gunpowder  to  be  ignited.  Defects  :  Action  slow  ;  charge  employed 
too  small ;  dangerous  to  lay.  Dangerous  to  recover  or  destroy  wlien  no 
longer  required.     Results  during  the  war  practically  nil. 

About  ten  years  later  the  Dutch  Government  carried  out  experi- 
ments with  mines  primed  with  Colonel  Ramstedt's  exploder,  viz.,  a 
bent  glass  tube  containing  a  small  plug  of  potassium  covered  with 
naphtha.  The  long  leg  of  the  tube  is  sealed,  and  the  short  leg  open, 
but  it  should  be  covered  with  a  thin  skin  diaphragm.  This  leg  is  in 
contact  with  the  priming  charge.  The  long  leg  is  carried  througli  tlie 
case  by  a  waterproof  joint,  and  is  exposed  to  the  sea  water.  Tliis  can 
be  covered  with  a  perforated  leaden  cap  which  is  bent  by  a  vessel 
striking  it,  thus  causing  the  tube  to  break,  and  water  to  get  at  the 
potassium,  igniting  the  charge.  Defects :  Action  rather  slow ;  dangerous 
to  lay;  does  not  remain  in  good  order  for  lengtliened  periods.  Dangerous 
to  recover  or  destroy  when  no  longer  i-equired. 

An  improvement,  suggested  by  the  writer,  consisted  in  surrounding 
the  projecting  glass  tube  with  a  perforated  brass  cylinder  containing  a 
small  weight  with  a  vertical  hole  fitting  over  the  tube ;  also,  in  filling 
the  cylinder  with  a  cement  slowly  soluble  in  water,  such  as  a  lieated 
mixture  of  sugar  and  chalk.  This  makes  the  mines  safe  to  lay,  as  the 
apparatus  only  becomes  active  after  the  period  necessary  for  dissolving 
the  cement.  Moreover,  the  charge  can  be  so  placed  in  the  case  that 
the  mine  turns  over  if  it  escapes  from  its  fastenings,  tiie  weight 
tumbles  out  of  the  cylinder,  the  latter  protects  the  glass  tube,  .-md  tlie 
mine  can  then  be  recovered  with  safety.  Defects  :  Action  sIom-,  and 
mine  does  not  remain  in  good  order  for  a  long  period. 


Chemical,  Frict'wnal,  Percussive.  205 

Frictionnl  Automatic  Mines. — Tlie  mine  invented  by  Mr.  E.  C. 
Singer  and  extensively  used  with  much  success  by  the  Confederates  in 
the  American  War  of  Secession,  is  a  good  example  of  tliis  type.  A 
friction  tube  and  small  priming  charge  is  secured  to  the  bottom  of  the 
case,  and  is  suitably  protected  from  the  salt  water  by  a  thin  dia- 
phragm. One  end  of  a  short  chain  is  attached  to  the  pull  ring,  the 
other  to  a  cast-iron  cover  resting  on  the  top  of  the  case.  A  central 
aperture  in  the  lid  surrounds  the  ring  for  the  lowering  line.  Until 
the  latter  is  withdrawn  the  mine  is  consequently  safe.  As  additional 
security  a  short  bight  of  the  chain  is  connected  with  a  safety  pin 
secured  to  the  bottom  of  the  case  or  to  the  mooring  chain.  The  last 
operation  is  to  withdraw  this  pin  by  a  line,  thus  making  the  mine 
active.  This  can  be  done  from  a  safe  distance.  The  line  can  be 
secured  to  a  float  and  the  moored  mine  remain  passive  as  long  as 
desired.  If,  however,  the  lid  has  been  thrown  off  in  the  mean  time, 
the  mine  would  explode  on  withdrawing  the  safety  pin.  Defects : 
Dangerous  to  recover ;  liable  to  self-destruction  by  tilting  in  a  strong 
current.     Easily  destroyed  by  sweeping  operations. 

Percussive  A^itomatic  Mines. — Several  patterns  of  this  type  have  been 
invented,  and  tried  experimentally  in  this  country ;  but  it  is  so  difficult 
to  insure  safety  when  recovering  the  mines  that  none  of  these  patterns 
have  been  adopted.  Most  of  these  apparatus  are  secret,  but  one  of 
them  which  was  invented  by  the  writer  can  be  described,  and  forms  a 
good  illustration  of  the  type.  The  bottom  of  the  mine  case  D  is  pro- 
vided with  a  circular  hole  to  which  the  apparatus  is  secured  by  bolts 
and  nuts.  The  apparatus  consists  of  a  cast-metal  liat-shaped  chamber  A, 
smaller  at  the  top  than  the  bottom,  and  carrying  a  tube  with  a  helical 
spring  h,  that  actuates  a  striker,  on  a  cap  c,  which  ignites  a  detonator 
and  the  priming  charge  in  P.  The  bottom  of  the  chamber  is  closed 
with  an  india-rubber  diaphragm  i,  carried  on  a  central  bolt  a;  by  a  suit- 
able nut  and  washer.  The  bottom  of  x  passes  through  a  lower  casting 
B  of  peculiar  shape  (see  sketch.  Fig.  90),  and  containing  in  its  lower 
portion  some  soluble  cement,  such  as  a  mixture  of  powdered  chalk  and 
burnt  sugar.  This  chamber  Z  has  orifices  communicating  with  the 
salt  water  outside.  The  mine  is  moored  by  the  ring  R.  Into  the  top 
of  X  is  screwed  a  small  spindle  of  brittle  steel,  with  an  eye  at  the  top, 
by  which  a  cord  connects  it  with  the  striker.  A  weight  W  rests  on 
the  nut.  This  weight  cannot  rock  in  the  upper  portion  of  A  when  in 
the  position  seen  in  sketch,  but  when  it  is  pulled  down  into  the  lower 
portion  its  movement  horizontally  is  only  cliecked  by  tlie  fragile  steel 
spindle. 

When  the  mine  is  first  laid  its  buoyancy  acting  against  the  mooring 
cannot  move  the  rod  x  ;  but  after  a  few  hours  the  cement  in  Z  dissolves, 


206 


Submarine  Miniiuj. 


the  rod  is  pulled  down,  the  spiral  spring  is  compressed,  and  the 
weight  W  is  brought  into  the  larger  portion  of  chamber  A.  If  a  vessel 
now  strike  the  mine  the  inertia  of  W  breaks  the  steel  spindle,  and  the 
striker  is  released  upwards,  exploding  the  mine.  Thus,  these  mines  are 
quite  safe  to  lay  out.  The  difficulty  is  to  raise  them  again  when 
required. 

The  plan  proposed  by  the  inventor  was  to  employ  a  small  explosive 
link  at  the  foot  of  the  mooring  line,  the  link  being  exploded  by  electri- 
city, and  to  carry  a  small  insulated  wire  to  a  position  of  safety,  say  100 


Fig.  HO. 


yards  away,  several  mine  wires  converging  on  one  point.  Also  to  so 
ballast  the  mine  that  when  it  is  released  from  its  mooring  it  shall  turn 
over  as  it  floats  to  the  surface.  The  pressure  of  the  water  acting  on 
the  rubber  diaphragm  and  the  weight  of  W  then  bring  the  apparatus 
into  the  safe  state  which  was  obtained  when  it  was  first  laid.  The 
position  of  R  can  be  seen  when  the  mine  floats  up.  If  home,  the  mine 
is  safe.  If  not,  the  case  should  be  destroyed  by  rifle  bullets,  and  the 
mine  sunk,  an  explosive  being  used  that  is  damaged  by  water.  Other 
means  than  electricity  can  be  used  for  releasing  the  mines  from  their 
moorings.  Defect  :  Difficult  to  recover  with  absolute  certainty  as  to 
safety. 

Electric  Aiiloinatic  Mines. — This  is  doubtless  the  best  and  most  reli- 


Electric  Automatic.  207 

able  type  of  the  .automatic  mine.  It  lias  been  adopted  by  several  of  the 
Continental  powers  in  one  form  or  another,  a  favourite  pattern  being 
the  invention  of  Pi'ofessor  Hirsch.  In  this,  each  mine  is  provided  with 
a  number  of  projections  or  nipples,  against  any  of  which  a  boat  or  vessel 
may  strike.  Each  nipple  consists  of  a  leaden  envelope  containing  a 
small  glass  phial  full  of  acid.  When  this  is  broken  it  is  arranged  that 
the  acid  shall  run  down  upon  two  electrodes,  thus  forming  a  voltaic 
couple.  Wires  from  the  holes  in  each  nipple  ai'e  carried  to  the  mine 
fuze,  which  is  consequently  exploded  directly  one  of  the  nipples  is  bent. 
Part  of  the  circuit  is  arranged  to  pass  through  a  loop  made  by  two 
wires  led  from  the  mine  to  a  safe  distance,  and  these  are  connected 
after  the  mine  is  laid,  and  when  it  is  desired  to  make  it  active.  Until 
this  has  been  done  the  mine  cannot  be  exploded,  but  it  can  be  damaged 
if  struck.  In  order  to  raise  such  a  mine,  it  is  only  necessary  to  recover 
the  loop,  and  to  disconnect  the  wires.  The  mine  is  then  safe  to  raise. 
Of  course  there  is  danger  that  a  faulty  connection  may  exist  inside  the 
mine,  and  it  would  be  more  assuring  to  have  the  source  of  electricity 
outside  it. 

This  leads  us  to  another  and  probably  the  best  pattern  of  the  elec- 
trical type  of  automatic  mine.  It  was  first  suggested  by  Sergeant- 
Major  Mathieson,  of  the  Royal  Engineers,  and  consists  of  the  usual 
electro-contact  mine  connected  with  a  voltaic  battery  in  a  suitable 
water-tiglit  box  which  is  submerged  near  to  the  mine,  but  far  enough 
from  it  to  allow  of  the  battery  being  raised  and  disconnected  with 
safety  before  raising  the  mine. 

A  number  of  mines  can  be  fired  in  this  manner  from  one  battery, 
and  the  recovery  of  the  latter  when  desired  can  be  easily  insured  by 
several  obvious  devices  without  using  a  marking  buoy. 

The  only  difficulty  in  connection  with  this  arrangement  has  been  the 
constancy  of  the  submerged  firing  battery,  which  is  apt  to  deteriorate 
if  the  water-tight  chamber  be  small. 

The  very  sensitive  low-resistance  detonators  that  have  been  intro- 
duced by  the  Danes  (see  page  117)  has  simplified  this  problem  immensely, 
as  a  small  number  of  cells  can  be  used,  and  the  cells  themselves  can  be 
of  moderate  size.  A  pattern  should  be  employed  that  is  known  by  ex- 
periment to  remain  in  working  order  for  lengthened  periods  without 
attention,  and  means  must  be  taken  to  prevent  loss  of  liquid  by  evapo- 
ration or  otherwise. 

The  same  mines  and  gear  generally  can  be  employed  for  this  system 
as  for  the  electro-contact  mines  controlled  from  a  distance,  but,  as 
already  stated,  it  is  unnecessary  to  provide  strong  and  costly  cases  for 
automatic  mines  of  any  pattern,  because  their  self-destruction  is  so 
readily  brought  about  by  countermining. 


208  Submarine  Mining. 

Electrical  automatic  mines  arranged  in  groups,  each  group  having  a 
submerged  voltaic  firing  battery,  are  doubtless  the  best  for  harbour 
defence,  their  only  defect  being  vulnerability  to  countermining.  For 
naval  purposes,  however,  the  mines  could  be  laid  more  rapidly  and  con- 
veniently if  each  were  complete  in  itself,  and  one  of  the  other  systems 
should  perhaps  be  chosen.  Moreover,  for  naval  purposes,  sucli  as 
blocking  the  waters  of  a  foe  by  mines,  it  is  advantageous  to  use  some 
arrangement  whereby  each  mine  will  take  the  desired  submersion 
automatically  when  it  is  laid.  Such  an  apparatus  has  been  invented 
by  an  officer  in  the  Royal  Navy,  but  it  is  a  secret,  and  cannot  therefore 
be  described  on  these  pages. 

A  good  pattern  of  automatic  mine  is  much  needed  for  our  harbour 
defences,  and  those  stations  that  require  tliem  should  be  supplied.  For 
instance,  important  stations  partly  surrounded  by  coral  reefs,  pierced 
in  several  places  by  navigable  guts  or  passages  too  far  from  the  land 
for  the  electrically  controlled  systems,  should  no  longer  remain  unpro- 
vided with  automatic  mines  of  a  simple,  strong  pattern,  not  likely  to 
"•et  out  of  order  or  to  require  repairs.  Surely  a  little  time  and  attention 
can  be  devoted  to  tliis  important  subject  by  those  concerned. 

"  Frame  Torpedoes.'" — When  shallow  waters  have  to  be  mined,  and 
when  the  current  always  flows  in  one  direction,  as  in  the  large  Ameri- 
can rivers,  a  very  useful  and  efficient  form  of  mine  is  the  frame  torpedo 
employed  by  the  Confederates  in  the  War  of  Secession.  A  framework 
of  strong  balks  is  made  and  a  mine  fixed  on  the  upper  end  of  each 
timber.  The  lower  end  of  the  frame  is  secured  by  short  chains  to 
several  sinkers,  and  the  upper  end  is  held  down  to  any  desired  sub- 
mersion by  a  chain  or  chains  to  a  smaller  sinker  or  sinkers.  The 
lower  end  of  the  frame  is  up  stream,  and  consequently  tlie  torpedoes 
ai-e  presented  to  any  vessel  advancing  up  the  stream.  Various  devices 
can  be  used  for  ignition  on  contact,  the  best  probably  being  some 
arrangement  whereby  a  plunger  is  forced  in  by  contact  witli  the  vessel, 
and  thereby  releases  the  striker  of  a  lock  action  inside  the  torpedo. 

The  size  of  the  torpedo  can  of  course  be  adjusted  so  as  to  carry  any 
desired  charge,  and  to  possess  any  required  buoyancy,  but  the  latter 
may  be  avoided  if  the  framework  possesses  sufficient  buoyancy,  due 
allowance  being  made  for  water-logging.  In  swift  currents  the  buoy- 
ancy must  naturally  be  greater  than  in  sluggish  streams.  Chains 
should  be  laid  up  stream  from  the  frames,  so  that  they  may  be  re- 
covered with  as  little  danger  as  possible  by  vessels  towing  them  up 
stream  to  some  spot  suitable  for  dismantling  tliem. 

Similar  mines  can  be  fixed  to  piles. 


209 


CHAPTER  XX. 
The  Attack  on  and  Drfenck  of  Mined  Waters. 

The  defence  of  mined  waters  must  usually  be  effected  by  a  powerful 
artillery  fire,  but  the  guns  must  be  of  the  proper  quality  for  their 
targets. 

The  necessity  of  mounting  heavy  ai-mour-piercing  guns  is  univer.sally 
accepted,  as  evidenced  by  the  costly  forts  and  batteries  which  have 
been  erected  throughout  the  world  wherever  harbour  defence  has 
received  attention. 

But  an  attack  on  mined  waters  must  be  delivered  by  small  craft  ; 
and,  as  it  is  not  desirable  to  crack  nuts  with  steam  liammers,  the 
artillery  to  ward  off  such  attacks  should  include  a  large  number  of 
quick-firing  guns,  such  as  the  Hotchkiss  or  the  Nordenfelt.  These 
guns  should  be  so  placed  on  shore  that  they  are  not  inconvenienced  by 
the  smoke  from  guns  of  heavier  calibre,  and  should  be  so  mounted  as 
to  remain  under  cover  until  the  moment  they  are  required.  Moreover, 
smokeless  powder  should  be  used  in  their  ammunition  (see  page  224). 
But  boat  attacks  should  often  be  met  afloat,  especially  where  the 
mined  waters  are  some  distance  from  the  shore.  In  such  event,  quick- 
firing  guns  should  be  mounted  on  a  number  of  small  steamers,  this 
defence  flotilla  being  kept  out  of  the  range  of  the  attacking  artillery 
as  long  as  possible. 

Steam  yachts  and  harbour  tugs  would  answer  well,  and  a  numlter  of 
quick-firing  guns  shovild  be  kept  in  store  for  their  armament. 

Assuming  that  the  defenders  possess  torpedo  boats,  these  should  not 
be  employed  in  repelling  boat  attacks.  Unless  they  are  nearly 
submerged  and  of  the  almost  invisible  type,  they  should  be  held  in 
reserve  to  act  against  large  vessels  during  the  later  stages  of  the 
operations  when  the  defenders'  artillery  has  been  crippled,  and  the 
waters  have  been  partially  cleared  of  mines.  At  such  a  time  a  reserve 
of  defensive  power  would  be  of  great  value.  As  attacks  upon  mined 
waters  are  probable  at  night,  the  defence  must  be  well  supplied  with 
powerful  electric  arc  lights  to  search  for  and  discover  the  positions  of 
the  attacking  flotilla  and  of  the  larger  vessels  in  support.  Those  lights 
P 


210  Submarine  Mining. 

whicli  are  used  principally  in  connection  with  the  artillery  should  be 
under  the  charge  and  control  of  the  battery  or  fort  commander. 
Those  again  which  are  provided  specially  to  aid  in  firing  the  mines 
at  the  correct  moment,  should  be  under  the  control  of  the  officer 
in  charge  of  the  mines.  "When  an  attack  has  been  developed,  the 
quick-firing  guns  of  the  foe  might  soon  destroy  the  electric  lights  on 
shore,  and  means  should  therefore  be  taken  to  use  plane  mirrors  as 
reflectors  when  the  foe  comes  to  close  quarters.  Thus,  when  the  lights 
are  used  for  searching  purposes,  the  costly  catoptric,  or  dioptric,  or 
catadioptric  lantern  can  be  exposed  ;  but  when  the  light  is  used  for 
illuminating  the  waters  near  at  hand,  tlie  lamp  should  be  lowered  under 
cover,  and  the  plane  mirror  raised. 

The  small  steamers  already  mentioned  would  act  on  outpost  duties 
in  advance  of  the  mined  waters,  and  the  search  lights  would  greatly 
assist  them.  Some  of  the  larger  patrolling  steamers  might  with 
advantage  themselves  carry  electric  lights,  say,  60  cm.  Mangin  lanterns 
containing  inclined  hand  lamps  and  arc  lights,  each  possessing  a  power 
of  about  20,000  standard  candles. 

The  first  step  taken  l)y  the  attack  would  be  a  heavy  artillery  fire, 
delivered  on  those  portions  of  the  defence  which  are  within  range  and 
exposed  to  fire.  This  would  be  done  by  daylight.  To  attempt  any 
boat  attack  before  the  artillery  defences  had  been  crippled  as  far  as 
possible  in  this  manner,  would  invite  defeat.  The  patrolling  boats 
could  not  hope  to  ofier  an  efiective  resistance  in  the  advanced  zone, 
except  for  a  short  time.  They  would  retire  as  soon  as  the  attacking 
flotilla  had  reached  the  waters  within  range  of  the  quick-firing  guns  on 
shore.  Good  range-finders  would  be  most  useful  at  this  stage,  as  also 
efficient  night  sights  for  the  quick-firing  guns.  An  attack,  which  must 
always  be  in  the  nature  of  a  forlorn  hope,  may  then  be  repelled  before 
any  serious  damage  is  done  to  the  mines  or  their  gear. 

Actual  war  can  alone  decide  whetlier  such  attacks  can  ever  succeed 
against  an  energetic  and  well-conducted  defence.  Operations  of  tliis 
nature  undertaken  in  time  of  peace  are  probably  more  misleading  than 
instructive.     They  leave  so  much  to  the  imagination  of  the  umpires. 

Creeping  for  Cables  and  destroying  them  by  means  of  explosive 
grapnels  fired  by  electricity  is  a  trustworthy  method  of  attack,  and  as 
it  can  be  undertaken  by  small  row-boats,  the  element  of  surprise  assists 
the  operation  on  dark  nights  when  boats  cannot  readily  be  discovered. 
In  order  to  throw  difficulties  in  the  way  of  such  a  method  of  attack, 
the  waters  in  front  of  the  mined  areas  should  be  liberally  sown  with 
pieces  of  old  cable,  lengths  of  chain,  &c.  ;  and  these  bottom  obstructions 
become  more  efficient  if  they  are  connected  with  small  sinkers  here  and 


Creeping,  Sv^eepivg,  Countermimng. 


211 


there,  and  with  submerged  buoys  between  the  sinkers,  the  loops  of 
dummy  cable  or  of  chain  thus  formed  near  the  bottom  l)eing  designed 
to  catch  the  grapnels. 

Sweeping  for  Mines  by  boats  in  pairs,  with  drift  ropes  or  nets 
between  them,  is  a  most  difficult  operation  to  carry  out  at  night,  and  it 
would  of  course  be  impossible  to  perform  it  successfully  by  day  under  a 
hostile  fire. 

The  Attack  by  Countermines  finds  many  advocates,  and  its  efficiency 
is  fully  believed  in  by  a  number  of  naval  officers  whose  opinions  on 
such  a  subject  should  carry  weight.  Nevertheless  it  cannot  be  denied 
that  the  methods  usually  adopted  in  Europe  for  laying  countermines 
are  crude,  and  that  any  of  a  number  of  small  accidents  which  are 
nearly  certain  to  occur  on  active  service  would  cause  the  failure  of  a 
boatload  of  countermines.  To  lay  a  string  of  mines  from  a  boat  is  a 
most  difficult  operation  at  the  best  of  times,  in  full  daylight,  and  to 
do  so  successfully  at  night,  during  the  excitement,  smoke,  and  turmoil 
of  an  actual  engagement,  when  a  single  bullet  may  cut  one  of  the 
exposed  electric  cables,  would  be  scarcely  less  than  a  miracle.     The 

Kq.91. 


Americans  are  developing  a  system  which  promises  to  act  much  better. 
It  is  proposed  to  employ  the  air  gun  now  being  perfected  by  Captain 
Zalinski,  United  States  artillery,  and  to  mount  three  of  them  on  a 
steamer  specially  adapted  for  countermining  and  other  siege  purposes 
(Fig.  91).  This  vessel  is  designed  to  have  a  moderate  speed,  a  draught 
of  15  ft.,  good  beam,  and  low  freeboard.  Her  displacement  to  be 
about  3500  tons,  and  her  under-water  hull  to  possess  an  extreme 
cellular  subdivision,  and  a  double  bottom  18  in.  deep,  extending  to  a 
height  of  2  ft.  above  the  water  line.  This  double  bottom  to  be  filled 
with  cocoa  fibre  cellulose,  which  quickly  swells  and  fills  any  shot-hole 
through  which  water  might  otherwise  enter.  Her  top  sides  to  be 
armoured  to  4  ft.  below  the  water  line,  and  her  deck  to  be  turtle- 
backed  and  covered  with  5  in.  of  steel,  the  armouring  weighing  a  little 
over  1000  tons  in  all.  Her  three  air  guns  to  be  capable  of  throwing 
shell  containing  100  lb.  charges  of  high  explosive  to  ranges  of  at  least 
two  miles,  and  larger  charges  to  shorter  distances. 

The  designer  considers  that  100  lb.  of  blasting  gelatine  will  destroy 
all  mines  within  a  radius  of  50  ft.      He  proposes  that  three  air  guns 
should  be  mounted  side  by  side  in  the  fore  part  of  the  vessel,  the  two 
p2 


212  Svhmartve  Minhig. 

outer  guns  being  so  arranged  that  tliey  can  be  traversed  a  few  degrees 
outside  the  central  line  of  direction. 

It  is  intended  that  the  vessel  shall  anclior  outside  the  waters  supposed 
to  be  mined  and  take  up  any  required  position  for  the  operation  of 
countermining.  The  range  being  settled,  the  outer  guns  can  then 
have  their  traversing  gear  so  adjusted  that  their  shells  shall  drop 
100  ft.  on  either  side  of  the  shell  from  the  central  gun.  A  volley 
being  fired,  the  range  is  altered  by  100  ft.,  and  another  volley  delivered. 
The  traversing  of  the  outer  guns  is  altered  when  required,  so  as  to 
retain  the  same  width  of  countermined  channel  at  all  the  ranges.  In 
this  way  a  channel  100  yards  wide  and  two  miles  long  can  be  counter- 
mined in  two  hours  without  shifting  the  vessel,  160  shell  being 
expended  per  mile.  If  desired,  shells  specially  fitted  with  releasable 
buoys  can  occasionally  be  discharged  from  the  outer  guns,  and  the 
channel  be  tlieveby  buoyed  as  it  is  cleared.  About  20  tons  of 
ammunition,  costing  6000^.,  would  be  expended  per  mile  of  cleared 
channel. 

Captain  Zalinski  states  that  the  range  is  practically  unaflected  by 
the  slight  alterations  in  the  elevation  of  tlie  guns,  which  would  be 
caused  by  the  vessel  pitching  at  her  moorings.  The  vessel  would 
carry  as  additional  armament  a  number  of  quick-firing  cannon  and 
machine  guns. 

It  is  evident  that  countermining  operations,  even  when  undertaken 
from  a  distance  by  such  a  vessel,  cannot  be  successfully  performed  by 
daylight  so  long  as  the  artillery  defences  remain  ;  and  considerable 
uncertainty  would  attend  the  operation  when  conducted  under  cover 
of  darkness,  liowever  carefully  the  ship  is  laid  by  compass  bearings  or 
by  lights  on  shore,  should  they  exist.  Sweeping  and  creeping  could 
never  be  undertaken  by  daylight,  within  range  of  the  shore,  so  long 
as  the  defence  retained  the  power  of  bringing  machine  gun  fire  to  bear 
upon  the  boats.  In  short,  the  whole  of  tlie  work  connected  with  the 
attack  on  mined  waters  is  so  diflftcult  and  hazardous  that  we  may  fairly 
doubt  the  probability  of  these  operations  ever  being  seriously  under- 
taken until  the  forts  and  batteries  have  been  demolished  and  the 
defence  thoroughly  demoralised.  Nothing  of  the  kind  occurred  during 
the  American  War  of  Secession,  when  the  vessels  either  ignored  the 
mines  and  took  their  chance,  or  attacked  the  stations  by  forces  landed 
for  this  purpose,  or  remained  outside  ;  and  of  tliese  three  courses,  the 
latter  was  generally  pursued. 

Ilhimination  of  Fortified  Ilnrhoiirs. — Nevertheless,  as  tlie  attack  of 
mined  waters  at  night  is  so  favourably  viewed  by  many  experts,  the 
defence  must  be  arranged   so  as   to   offer  a  strong  resistance  at  that 


Electric  Lights. 


213 


time,  and  the  illumination  of  the  mined  waters  and  of  the  waters  in 
advance  of  the  mines  becomes  important. 

The  French  have  devoted  much  attention  to  this  subject,  and  have, 


y\ 


'I  \ Yk 

\ 
\ 


■1^ 


// 

/ 

// 

//  /   / 


y//\ 


^^4ji»= 


///I 


it  is  believed,  erected  a  number  of  powerful  electric  lights  at  each  of 
their  sea  fortresses.  We  have  done  the  same,  but  in  a  less  pronounced 
manner:  and  when  we  consider  the  great  cost  of  these  lights,   their 


214 


Submarine  Mining. 


exti-eme  vulnerability  to  machine  and  other  fire,  and  the  inconvenience 
to  the  defence  flotilla  which  their  injudicious  use  may  often  occasion, 
it  would  appear  desirable  to  limit  the  electric  lights  to  a  moderate 
number  at  each  harbour.  Some  experts  consider  that  there  cannot  be 
too  many  of  them.  This  is  probably  a  mistake.  As  before  stated, 
such  a  light  should  act  direct  from  its  lantern  when  used  for  searching 
purposes ;  but  when  a  liostile  flotilla  comes  to  close  quarters,  these 
expensive  lanterns  should  be  lowered  under   cover   and   an   arrange- 


ment raised  whereby  the  ray  of  light  can  bo  reflected  in  any  desired 
direction  by  a  cheap  plane  mirror  that  can  l)o  readily  replaced  when 
broken. 

The  following  arrangement  has  been  worked  out  by  Messrs.  Day, 
Summers,  and  Co.,  Southampton,  from  a  design  by  the  writer.  The 
apparatus  is  placed  in  a  pit  behind  a  parapet.  A  masonry  pedestal  in 
the  centre  of  the  pit  (see  Figs.  92,  93,  and  94)  carries  a  pivot  round 
which  a  turntable  F  revolves  on  rollers  G.      The  pivot  is  secured  to  a 


Electric  Lights. 


215 


v'uv^  oil  whicli  G  (!  roll,  and  rouiul  wliicli  is  placed  a  brake  sii'a})  t'ur 
liolding  the  turntable  by  the  handle  K  wiienever  recjuired.     The   turn 


table  can  be  revolved  by  a  handspike  H  directly  K  is  released.     A  car- 
riage, fixed  to  the  turntable,  supports  on  the  trunnions  D  two  girders 


216 


Submarine  Mining. 


framed  together  at  their  ends  and  connected  by  a  ring  at  the  centre. 
This  frame  can  be  clamped  in  any  position  by  the  arc  and  screw  E.  An 
electric  lantern  A  is  supported  at  one  end  of  the  framed  girders  on 
trunnions  L,  and  is  capable  of  vertical  adjustment  by  tiie  handwheel  M. 
A  plane  mirror  B  is  supported  on  trunnions  N  at  the  other  end  of  the 
frame  and  can  be  adjusted  vertically  by  tlie  handwheel  0,  or,  if  Hashing 
signals  are  required,  the  mirror  can  be  moved  quickly  in  altitude  by  the 
handle  P.     A  platform  Q,  bolted  to  the  carriage,  supports  the  operator. 

When  the  apparatus  is  out  of  action  the  frame  is  brought  into  a 
horizontal  position,  and  everything  is  then  under  the  crest  of  tiie 
parapet.  When  it  is  to  be  used  as  a  searcli  light  the  lantern  end  of 
the  frame  is  raised  and  the  light  works  direct  from  its  lantern  over  the 
crest  of  the  parapet.  When  it  is  desired  to  lower  the  lantern  and  pro- 
tect the  light  the  carriage  is  turned  round,  the  lantern  lowered,  and  the 
mirror  raised.  The  electric  connections  are  not  shown.  There  is  no 
difficulty.  The  wires  pass  through  the  centre  of  the  pedestal  and  the 
pivot  and  are  carried  direct  to  the  lantern,  thus  avoiding  any  sliding 
connections  outside  the  lantern. 

There  is  a  certain  loss  of  light  when  a  mirror  is  used.  The  quantity 
of  light  reflected  from  polished  metal  surfaces  is  greatest  when  the 
angle  of  incidence  (between  the  ray  of  light  and  the  normal  to  the 
surface)  is  small,  but  an  exactly  opposite  result  is  obtained  with  non- 
metallic  surfaces,  such  as  water,  glass,  &c.  The  percentages  of  light 
reflected  from  various  surfaces  are  as  follows  : 


Table  XXXIII. 


Angle  of  incidence 

Water 

Glass      

Polished  silver 


75deg. 
21  p.c. 
30  p.  0. 


60  deg. 
6.5  p.c. 
11.2  p.c. 
nearly  90  p.c. 


45  deg. 
4.5  p.c. 


30  deg.  and  unde 
1.8  p.c. 
2.5  p.c. 


Glass  with  a  silvered  back  acts  nearly  as  efliciently  as  polished  silver, 
and  the  silver  does  not  tarnish,  the  air  being  thoroughly  excluded  from 
it.  Glass  is  therefore  greatly  preferable  to  metallic  mirrors.  At  long 
ranges  there  is  a  loss  of  light  due  to  dispersion  caused  by  want  of  abso- 
lute parallelism  between  the  two  glass  surfaces,  and  I  have  calculated 
that  this  loss  reduces  the  efficiency  of  a  glass  mirror  as  per  following 
Table : 

Table  XXXIV.— Glass  Mirrok  Silvered  on  the  Back. 


Angle  of  incidence 
Efficiency  at  short  range. 
„      ,,      long       „     . 


I  deg.  and  under 
90.9  deg. 


Electric  Lhjld  Reflectors.  217 

These  results  were  obtained  thus  : 

L^t  a  ray  of  light,  power  100,  fall  ou  a  glass  mirror   at  an  anyle   of 
incidence  45  deg.  (see  Fig.  95),  4.5  per  cent,  will  then  be  reflected  (see 


Frontoroiass  \\\ 

yi;9  ds . 

\/           Plain  surface 

"X               \    ft 

Cadi  of  Glass        Iv 

«99S.D 

Table)  from  the  front  surface,  and  95.5  per  cent,  will  penetrate  the 
glass  to  the  back  surface  in  a  direction  depending  upon  the  index  of 
refraction  (about  1.53  for  plate  glass),  so  that  the 

Sin  angle  of  incidence  -^  sin  angle  of  refraction  —  index, 

or  in  above  example, 

Sin45deg.-^sin  a=1.53, 
consequently 

a  — 27  deg.  30  min. 

From  Table  XXXIII.  the  amount  of  light  reflected  from  the  silvered 
surface  will  therefore  be  90  per  cent,  of  95.5,  say  86,  and  nearly  84  of 
this  will  go  away  from  the  top  surface  of  the  glass  nearly  parallel  to  the 
4.5  ray.  As,  however,  the  glass  surfaces  can  never  be  absolutely 
parallel,  these  two  rays,  as  well  as  the  smaller  third  ray,  will  gradually 
diverge,  and  the  power  of  the  reflected  ray  at  45  deg.  will  therefore 
never  exceed  84  per  cent,  except  at  short  ranges. 

Similarly,  it  can  be  shown  that  the  principal  reflected  ray  for 
angles  of  incidence  of  30  deg.  and  under,  and  60  deg.  and  75  deg.,  are 
86  per  cent.,  77  per  cent.,  and  59  per  cent,  respectively.  These  figures 
demonstrate  the  advantage  of  so  using  glass  mirrors,  that  the  angle  of 
incidence  is  small.  The  arrangement  already  described  does  this,  the 
mirror  being  so  placed  that  the  reflected  ray  when  directed  on  the 
horizon  from  an  emplacement  near  the  water  level  makes  an  angle  of 
36  deg.  with  the  principal  axis  of  the  frame  carrying  the  mirror  and 
lantern,  the  angle  of  incidence  being  only  18  deg.  Not  less  than  86 
per  cent,  of  the  light  is  therefore  reflected  (see  Table)  when  the  outer 
glass  surface  is  clean  and  dry. 

Means  should  be  provided  for  rapidly  replacing  the  plane  mirror  if  it 
be  shot  away.  An  arrangement  designed  by  Major  M.  T.  Sale,  O.M.G., 
R.E.,  in  which  a  disc  of  silvered  copper  is  stretched  on  a  frame  like  a 
drum-head,  has  been  found  to  answer  admirably  as  a  plane  mirror.  It 
remains  efiective  after  being  hit  by  bullets  or  shrapnel.  This  was 
proved  conclusively  by  recent  experiments  carried  out  at  Okehampton 
and  reported  in  the  Times. 


218  Sicbmarine  Mining. 

Passing  to  the  lantern,  tlie  catoptric  arrangement  designed  by  Colonel 
Mangin,  of  the  French  Corps  du  Genie,  is  probably  the  best,  although 
it  is  said  that  a  good  dioptric  lamp  has  been  known  to  beat  it.  But 
the  focal  distance  of  the  carbons  is  so  much  shorter  in  most  of  the 
lanterns  fitted  with  concentric  prismatic  rings  of  glass  that  it  is  most 
difficult  to  obtain  and  keep  the  light  at  true  focal  length.  In  the 
catoptric  lanterns  the  focal  distance  can  be  much  longer  without  greatly 
increasing  the  cost.  Moreover,  fairly  good  results  can  be  obtained  by 
cheaper  arrangements  than  Colonel  Mangin's,  one  of  the  best  of  these 
being  the  result  of  Captain  Cardew's  scientific  labours  at  Chatham.  In 
these  less  costly  designs  for  a  catoptric  lantern,  efficiency  appears  to 
depend  upon  the  size  of  the  curved  reflector,  and  it  is  interesting  to 
note  that  similar  results  were  obtained  in  1855,  as  the  outcome  of  the 
investigations  made  by  General  Cator's  committee,  appointed  by  the 
Director-General  of  the  Ordnance.  After  trying  various  forms  of 
parabolic  and  other  reflectors,  it  was  then  agreed  that  the  best  was  a 
large  spherical  surface  about  3^  ft.  in  diameter,  and  forming  50  deg.  of 
a  sphere  8  ft.  in  diameter.  The  long  focal  distance  obtained  from  the 
use  of  such  a  spherical  surface  appeared  to  give  better  results  than  the 
theoretically  perfect  surface  of  a  paraboloid  where  the  focal  distance  is 
necessarily  shorter ;  and  this  is  especially  true  when  the  electric  light 
is  used,  tlie  carbon  points  occupying  a  certain  dimension.  The  sine  of 
the  angle  of  dispersion  is  equal  to  the  radius  of  the  dimension  of  the 
source  of  light  divided  by  the  focal  distance,  and  this  consideration 
demonstrates  the  advantage  of  using  a  lantern  (whether  catopric  or 
dioptric)  with  a  long  focal  distance. 

The  local  glare  caused  by  a  powerful  electric  light  is  so  great  that  the 
observer  should  be  located  at  some  distance  from  it,  and  it  may  fre- 
quently occur  that  he  should  be  stationed  well  to  the  front  and  afloat. 
The  light  should  be  under  his  control,  if  possible,  and  the  simplest  way 
to  do  this  is  to  erect  two  single  needle  galvanometers  on  the  carriage  of 
the  apparatus,  and  to  connect  them  with  the  observer.  A  deflection  to 
the  right  or  left  on  one  needle  can  indicate,  elevate,  or  depress  ;  and  on 
the  other  needle  traverse  right  or  left.  In  this  manner  a  search  light 
on  shore  may  be  under  the  control  of  an  officer  in  command  of  the 
defence  flotilla,  the  steamer  being  anchored  in  a  suitable  position  and 
an  electric  cable  taken  to  it.  One  or  two  good  search  lights  are  pro- 
bably sufficient. 

In  addition  there  should  bo  one  or  two  electric  lights  for  providing  a 
fixed  ray  across  the  waters  in  advance  of  the  mine  fields.  These  lights 
should  not  be  displayed  until  the  attack  has  been  pushed  to  the  waters 
in  front,  and  until  the  defence  flotilla  has  retired  in  rear  of  the  ray  or 


Lucigen  LIglits.  219 

lane  of  illuininatod  M-ater.  Tlie  defence;  will  then  be  enabled  to  open  a 
heavy  fire  on  any  attacking  boat  that  may  venture  across  the  lighted 
area. 

When  the  attacking  forces  have  so  far  developed  their  operations  the 
defence  would  derive  great  assistance  from  the  employment  of  powerful 
floating  lights,  and  the  Lucigen  Light  Company  is  endeavouring  to  per- 
fect an  apparatus  of  this  nature.  A  "  triplex  Lucigen  "  has  a  power  of 
10,000  standard  candles,  and  is  stated  to  be  capable  of  illuminating  an 
area  equal  to  a  quarter  of  a  square  mile — say  a  circular  area  half  a  mile 
in  diameter. 

Probably  the  best  way  to  use  the  Lucigens  for  illuminating  harbour 
entrances  will  be  to  fit  them  on  small  steam  pinnaces,  each  so  built  that 
the  boat  cannot  easily  be  seen  or  struck,  the  hull  being  nearly  sub- 
merged, and  having  a  steel-faced  turtle-backed  deck.  The  air-compressing 
machinery  required  for  the  light  could  be  driven  by  steam  taken  from 
the  boiler  for  the  propelling  machinery,  and  the  boat  could  easily  be 
fitted  with  an  air  receiver,  and  with  a  tank  to  carry  oil  for  replenishing 
the  Lucigen  as  required. 

Such  a  boat  could  be  moored  suitably,  so  that  in  the  event  of  an 
attack,  the  powerful  lights  carried  would  be  displayed,  and  the  attack 
be  thereby  clearly  seen  by  the  gunners  of  the  defence,  both  on  shore 
and  afloat. 

Electric  lights  are  most  useful  for  search  and  discovery  work,  but  they 
illuminate  small  areas  intensely,  leaving  the  rest  in  deep  shadow.  If  they 
were  supplemented  by  lights  like  the  Lucigen,  directly  an  attack  de- 
veloped, the  whole  of  the  water  could  be  illuminated  and  the  power  of 
defence  be  greatly  augmented.  There  should  be  no  difliculty  in  screen- 
ing the  light  of  each  Lucigen,  so  that  it  would  be  directed  only  in  a 
desired  direction,  and  the  armed  guard  boats  of  the  defence  might  take 
up  positions  in  the  dark  area  in  rear  of  the  lights  as  soon  as  an  attack 
had  been  discovered,  either  by  observers  on  shore  or  afloat.  The  attack 
would  thus  be  delivered  under  great  disadvantages,  for  a  well-lighted 
area  would  have  to  be  crossed,  which  would  be  swept  by  the  fire  of 
machine  guns  afloat,  and  of  quick-firing  cannon  in  the  shore  batteries. 

Obstructions. — Just  as  the  mines  themselves  form  a  grand  obstruction 
to  the  passage  of  large  vessels  and  thereby  assist  greatly  in  the  defence 
of  a  maritime  fortress,  so  smaller  obstructions  can  be  usefully  employed 
to  impede  and  perhaps  prevent  the  passage  of  small  craft  whose  aim 
may  be  to  attack  the  mines. 

Floating  Nets  can  be  used,  and  if  small  steamers  get  among  them  the 
propellers  are  often  fouled,  the  boats  become  temporarily  helpless,  and 
may  be  destroyed  by  a  well-directed  fire  from  quick-firing  or  other  guns. 


220  Submarine  Mining. 

Nets  can,  however,  be  readily  passed  if  seen,  small  lengths  of  chain 
being  thrown  upon  them  from  the  boats,  which  effectually  sinks  them. 

Bootns,  when  well  made,  are  probably  the  most  effective  passive 
obstruction  against  the  passage  of  boats.  They  should  invariably  be 
formed  of  a  double  line  of  balks  at  such  a  distance  apart  that  a  boat 
which  succeeds  in  jumping  or  passing  through  the  front  line,  is  brought 
up  by  the  second  line.  The  two  lines  should  be  connected  frequently 
by  cross-beams,  the  whole  presenting  the  appearance  of  a  large  floating 
ladder.  Wire  ropes  or  chains  should  run  along  each  line  and  be  con- 
nected to  the  main  anchors  at  the  ends  of  the  boom.  Stream  anchors 
should  also  be  connected  to  the  boom  at  intervals  in  order  to  keep  it  in 
position  when  the  tidal  or  other  currents  flow  across  it,  and  during 
stormy  weather.  If  such  a  boom  be  deficient  ia  buoyancy,  empty  casks 
can  be  lashed  to  it  at  intervals.  An  attacking  flotilla  generally  tries 
to  destroy  such  an  obstruction  by  means  of  small  charges  attached  to  it 
and  then  fired  by  electricity  through  a  length  of  insulated  wire.  Some 
experts  consider  that  such  a  boom  should  be  moored  on  the  waters 
immediately  in  front  of  the  mined  area,  and  that  the  fixed  ray  from  an 
electric  light  should  be  directed  upon  it  or  upon  the  water  immediate. y 
in  front  of  it.  It  is  perhaps  better  to  place  it,  as  well  as  the  ray  of 
light,  some  distance  in  front  of  the  mines,  whose  position  is  not  then 
demonstrated  with  such  precision.  The  boom  should  be  just  behind 
the  ray  of  light,  but  should  boats  attempt  to  fire  charges  on  the  boom 
the  light  should  be  thrown  upon  them,  and  every  means  taken  to  pre- 
vent the  explosion  of  the  charges.  The  boom  should  consequently  be 
enfiladed  by  some  quick-firing  guns  of  the  defence,  and  if  a  few  circuit- 
closers  be  connected  to  the  boom  in  such  a  way  (to  be  described 
presently)  that  a  signal  is  given  on  shore  when  a  boat  comes  against  the 
boom,  the  defenders  will  know  when  to  open  fire  and  how  to  direct 
it,  even  in  darkness  and  when  no  object  is  seen.  This  idea  is  similar 
to  " automatic  artillery  fire"  advocated  by  the  writer  in  1883.*  The 
approaches  to  a  boom  can  also  be  sown  with  small  mines,  specially 
designed,  and  having  a  proper  submersion  for  acting  against  small  craft. 

When  there  is  but  little  rise  and  fall  of  tide,  either  electro-contact  or 
automatic  mines  may  be  employed,  care  being  taken  when  the  latter 
are  used  that  the  defence  flotilla  keeps  clear  of  them,  leading  lights  on 
shore  being  employed  for  this  purpose.  But  a  very  small  tidal  rise  and 
fall  causes  such  mines  to  become  useless  at  high  water,  unless  they  are 
awasii  at  low  water,  which  is  not  permissible,  as  the  mines,  if  electric, 
would  be  constantly  signalling  by  wave  action,  and  if  automatic  would 
destroy  themselves  in  rough  weather. 

•  See  paper  read  at  the  Royal  United  Service  Institution,  March  14,  1S84. 


Booms  and  Boat  Mines. 


221 


In  tidal  waters  INIajor  R.  i\I.  Ruck's  system  of  rise  and  fall  mines 
(already  described  on  pages  70  and  73)  may  perhaps  be  applied  to  boat 
mines,  but  it  would  probably  be  better  and  certainly  less  costly  to 
attach  mines  to  the  boom  itself,  and  to  arrange  so  that  each  shall  be 
exploded  when  a  boat  comes  into  contact.  This  action  can  be  secured 
in  the  following  manner. 

The  boom  may  be  formed  of  a  series  of  rafts  of  timber,  connected 
together  by  two  wire  ropes  or  chains,  one  along  the  front,  the  other 
along  the  rear.  To  the  front  of  each  raft  a  wire  is  stretched,  one  end 
of  this  wire  being  fixed  to  a  special  form  of  circuit-closer  which  is 
actuated  by  a  pull  on  the  wire,  the  other  end  being  secured  to  a 
spring  that  keeps  the  wire  in  tension.  This  spring  can  be  secured  to 
the  back  of  the  spar  raft. 

A  single  cable  from  a  distant  firing  battery  leads  to  each  ( ircuit- 
closer  in  turn,  thence  to  the  mine  which  that  circuit-closer  explodes.  The 
circuit-closer  can  be  placed  either  on  the  front  or  the  back  of  the  raft ; 
the  pull-wire  in  the  latter  case  being  led  through  a  pulley  at  each  end 
of  the  front  spar. 

The  explosion  of  the  mine  does  not  injure  the  raft  or  the  circuit- 
closer,  but  it  destroys  the  boat  whose  bow  causes  the  pull  on  the  wire 
by  coming  into  contact  with  it.     Fig.  96  shows  the  arrangement. 

F,9  ,97 


The  outrigger  is  provided  with  an  iron  eye  about  8  ft.  behind  the 
mine,  and  a  rope  being  previously  secured  to  the  centre  of  the  front 
log  and  its  end  secured  to  the  back  log,  this  end  is  passed  through  the 
eye  on  outrigger,  and  the  spar  then  thrust  out ;  the  inner  ends  of  the 
spar  and  of  rope  are  finally  secured  to  the  centre  of  the  back  log.  The 
electrical  joint  between  mine  wire  (which  is  stapled  in  a  groove  along 
the  under  side  of  the  outrigger)  and  circuit-closer  wire  is  then  connected 
up.  By  these  means  another  mine  on  its  outris-ger  can  readily  be  con- 
nected up  in  boom  to  replace  one  that  has  exploded. 

Fig.  97  shows  a  sectional  view  of  a  raft  and  mine.  T  he  rafts  would 
be  connected  up  in  line,  on  a  beach,  just  below  high- water  mark,  com- 
mencing work  on  a  falling  tide.  The  mine  and  its  outrigger  spar  would 
be  connected  up  separately  when  the  boom  is  in  place.  The  small 
insulated  wire  to  circuit-closer  and  to  mil  e  would  be  fixed  in  grooves  to 
the  spars  by  small  staples. 


222  Submarine  Mining. 

The  rafts  being  connected  together  in  boom,  they  are  towed  out  as 
soon  as  the  tide  floats  them,  and  taken  to  their  position  on  the  iiiino 
field,  a  large  anchor  having  previously  been  laid  and  buoyed.  One  end 
of  the  boom  is  secured  to  the  mooring  line  of  this  anchor.  The  boom 
is  then  stretched  into  its  position,  the  wire  ropes  being  made  as  taut 
as  possible,  and  a  second  large  anchor  laid,  and  its  mooring  line 
secured  to  the  far  end  of  the  boom.  Stream  anchors,  when  required, 
are  now  laid,  and  their  mooring  lines  secured  to  the  front  and  back  of 
the  boom,  between  the  rafts. 

The  electric  cable  is  then  connected  to  the  near  end  of  boom,  and  is 
laid  to  shore.  The  raft  mines  on  their  spars  are  brought  up  by  another 
boat,  and  are  lashed  in  position,  one  on  each  raft.  This  operation  can 
be  performed  at  the  same  time  that  the  electric  cable  is  being  laid. 

By  proceeding  in  this  manner,  most  of  the  work  is  done  on  shore, 
and  a  great  deal  of  it  can  be  done  permanently,  the  rafts  being  stacked 
at  the  depot  ready  for  use  at  any  moment. 

The  principal  cost  of  these  arrangements  is  that  of  the  spars  and 
materials  used  in  the  boom.  As  before  stated,  a  boom  of  some  kind  is 
essential  to  ward  off  boats,  and  small  mines  of  some  sort  in  front  of  the 


boom  or  attached  to  it,  add  greatly  to  the  efficiency  of  the  defence. 
The  above  arrangement  is  therefore  economical,  because  it  obviates  the 
use  of  sinkers,  mooring  lines,  &c.,  for  these  mines  ;  and  the  circuit-closers 
and  mine  cases  being  almost  invulnerable  in  countermining,  the  defence 
against  boat  attack,  produced  by  this  design,  is  strong;  It  more- 
over provides  against  the  difficulties  engendered  by  the  rise  and  fall 
of  tide. 

In  the  event  of  tlie  number  of  spars  available  being  limited  and  in- 
sufficient to  form  a  boom,  as  described,  the  following  alternative  design 
may  be  used.  It  is  more  economical  in  material,  but  not  so  trustworthy. 
This  arrangement  is  shown  in  Figs.  98  and  99.  It  consists  of  a  log  and 
a  cross-spar  projecting  a  few  feet  beyond  the  centre  of  the  former,  and 
secured  there  by  means  of  two  wire  ties. 

An  outrigger  spar  is  lashed  to  the  cross-spar,  and  projects  to  the 
front  a  few  feet  more. 

The  circuit-closer  and  pull-wire  form  a  projecting  triangle  to  the  end 
of  the  cross-spar,  to  whicli  they  are  secured  by  a  small  pulley,  not  shown 
on  the  drawing. 

Elasticity  in  tlie  pull-wire  can  b(>  obtained  by  securing  the  pulley  to 


Boovis  and  Boat  Mines. 


223 


the  cross-bar  end,  hy  means  of  a  strong  india-ruLboi-  strop,  or  by  any 
other  simple  spring. 

The  mine  is  suspended  from  the  end  of  the  out-rigger  spar. 

The  electrical  arrangements  and  the  mode  of  mooring  are  similar  to 
those  already  described  for  the  boom,  composed  of  rectangular  rafts. 

The  stream  moorings  would  have  their  lines  secured  to  the  wire  rope 
at  the  point  of  junction  of  two  rafts,  and  the  end  moorings,  and  electric 
cable  to  those,  would  be  arranged  precisely  as  in  the  former  example. 

The  circuit-closer  is  shown  on  Figs.  100  and  101.  It  consists  of  an 
iron  tube  provided  with  a  movable  end-piece,  to  which  is  secured  one 


of  my  patent  spring  ring  contact-makers.  The  other  side  of  the  ring 
is  held  by  a  bolt  that  crosses  the  iron  tube,  the  ends  of  the  bolt  lying 
flush  with  the  outside  surface  of  the  tube.  The  two  electric  wires  are 
led  through  a  pressure  plug  consisting  of  two  iron  discs,  an  india-rubber 
plug,  and  a  screw  bolt  and  nut  for  compressing  same,  the  nut  being 
turned  by  a  box  spanner  from  the  tube  end.  By  such  an  arrangement, 
the  plug  forms  a  good  water-tight  joint  both  for  the  tube  end  and 
for  the  wire  entrances.  Also,  the  plug  rests  solidly  on  the  before- 
mentioned  cross-bar,  and  cannot  therefore  be  driven  in  on  the  contact 
spring  by  the  pressure  produced  by  tiie  explosion  of  a  countermine, 
or  of  a  neighbouring  mine. 

The  end-piece  and  part  of  the  iron  tube,  are  surrounded  by  an  india- 
rubber  tube  lashed  to  each  of  them.  This  allows  the  end-piece  to  be 
pulled  out  for  a  short  distance  by  a  pull  on  the  wire,  and  the  elasticity 


224  Submnrine  Mining. 

of  the  in(lia-rul)l)er  tulie  helps  tlie  elasticity  of  tlio  spring  ring  to  pull 
the  end-piece  back  to  its  normal  position,  thus  reopening  the  contact 
points,  and  insulating  the  brancli  wire  from  the  electric  cable  if  the 
mine  be  tired,  or  bringing  everything  back  into  the  normal  condition  if 
the  mine  be  not  fired.  The  latter  occurs  when  the  firing  battery  has 
been  purposely  disconnected,  in  order  that  the  system  may  be  tested 
by  bumping  each  raft  in  turn  by  a  defence  boat,  a  test  battery  and 
galvanometer  only  being  in  circuit  on  shore,  during  such  an  opera- 
tion. 

The  circuit-closer  is  fixed  to  a  spar  or  other  object  by  means  of  a  crosi--- 
bolt  carried  through  a  hole  in  the  tube  at  the  end  furthest  from  the 
end-piece.  In  order  to  prevent  the  circuit-closer  being  unduly  strained 
by  the  bumping  tests,  two  side  links  (not  shown  on  the  drawing)  are 
provided,  which  hinge  on  the  long  cross-bolt.  These  links  connect  with 
another  cross-bolt  engaging  in  the  hole  provided  in  the  end-piece  for 
the  pull-wire,  the  hole  being  made  of  a  sufficient  length  and  size  for  this 
purpose  (see  Fig.  101). 

The  arrangement  of  end-piece,  ikc,  is  designed  to  form  an  efficient 
protection  to  the  apparatus  against  countermining,  but  it  is  of  no  use 
to  make  the  circuit-closer,  raft,  and  pull-wire  impervious  to  damage  by 
countermines,  unless  the  mine  be  so  also.  The  inventor  has,  therefore, 
taken  much  trouble  to  design  an  arrangement  for  the  charge  which  shall 
be  safe  against  countermining. 

The  charge,  about  20  lb.  of  wet  slal)  gun-cotton,  is  firmly  braced  be- 
tween two  iron  plates  by  bolts  and  nuts,  and  the  priming  charge  of  dry 
gun-cotton  is  placed  in  a  short  length  of  boiler  tube,  the  end  of  which 
is  closed  by  an  insulated  plug  for  the  wire  entrance.  This  plug  has  a 
circular  rim  between  which  and  the  tube  end  an  external  leather 
washer  is  pressed  by  two  small  studs  secured  to  the  top  plate  of  the 
charge.  The  wet  gun-cotton  is  cut  away  centrally  so  as  to  fit  against 
the  tube  containing  the  priming  charge,  and  a  hole  in  tlie  top  plate 
coincides  therewith.  A  '20  lb.  charge  will  act  efi'ectively  against  boats 
to  a  distance  of  10  ft.,  and  the  rafts  can  therefore  be  from  20ft.  to 
25  ft.  in  length.  The  apparatus  is  manufactured  by  ]\Tessrs.  Elliott 
Brothers,  London. 

Cribs  of  Timbers  filled  witli  stones,  and  otlier  obstructions  of  the 
kind,  can  be  used  when  it  is  desired  to  picvent  boats  passing  over 
shallow  waters. 

Jioaf.  Dp/pnce. —  Eut  the  best  defence  against  boat  attack  is  an  active 
boat  defence.  Should  this  collapse  or  be  non-existent,  the  best  systems 
of  passive  obstruction  must  fall  before  an  enterprising  foe. 

Smofi-eless  Powder. — The  employment  of  sucli  powder  (see  page  209)  is 


Smokeless  Poivder.  225 

now  being  carefully  tried  by  Lord  Armstrong,  who  in  a  recent  speech 
said  : 

"  A  new  departure  has  been  made  in  the  manufacture  of  powder 
....  for  our  quick-liring  guns.  It  is  made  by  the  Chilworth  Com- 
pany ....  and  iiotwithstanding  that  the  charges  have  been  reduced 
in  weight   by    about  one-third,    we   have    obtained  velocities    of    from 

2300  ft.  to  2400  ft.  per  second,  as  compared  with  2000  ft with 

other  powders.  This  new  powder,  moreover,  leaves  no  residue  in  the 
gun  to  interfere  witii  the  essential  requirement  of  rapid  loading,  and 
the  smoke  has  been  so  far  reduced  as  to  present  little  obstacle  to  the 
sighting  of  the  guns  in  action. 

"  These  are  advantages  which  can  scarcely  be  over-estimated." 


226 


CHAPTER  XXI. 

Torpedoes. 

As  submarine  mining  officers  not  unfrequently  have  the  charge  and 
direction  of  torpedoes  employed  in  harbour  defence  and  actuated  from 
shore,  a  treatise  on  submarine  mining  would  not  be  complete  without 
a  chapter  on  this  subject.  The  following  information  is  chiefly  derived 
from  articles  published  in  Engineering,  1887,  1888. 

Torpedo  Batteries. — The  employment  of  torpedoes  in  batteries  spe- 
cially constructed  for  them  has  often  been  recommended  for  the  defence 
of  narrow  channels,  entrances  to  harbours,  kc,  and  this  method  has 
been  adopted  by  some  nations  in  certain  favourable  situations. 

Tlte  Whitehead  Torfedo  has  been  adopted  as  a  naval  arm  by  so  many 
nations,  and  has  received  so  much  attention  for  a  long  period  of  years, 
that  it  has  probably  been  brought  to  the  maximum  state  of  efficiency 
obtainable  from  it.  It  is  so  well  known  that  a  detailed  description  is 
unnecessary,  but  it  will  be  as  well  to  note  some  of  its  chief  chai-ac- 
teristics,  and  especially  those  which  are  defects  inherent  to  the  inven- 
tion. 

The  case,  formed  of  steel,  or  of  a  very  strong  alloy,*  is  from  11  in. 
to  16  in.  in  diameter,  has  a  length  of  about  10  diameters,  is  circular 
in  cross-section,  and  is  pointed  at  each  end.  It  weighs  about  600  lb., 
and  carries  a  charge  of  from  40  lb.  to  70  lb.  of  high  explosive.  It  is 
propelled  by  two  screws,  one  abaft  the  other,  worked  in  opposite  direc- 
tions and  driven  by  a  self-contained  engine  and  a  reservoir  of  highly 
compressed  air  possessing  a  potential  energy  of  about  \  million  foot- 
pounds. A  regulating  valve  causes  the  engine  to  be  driven  at  any 
desired  speed.  This  valve  can  be  so  adjusted  that  the  mean  speed  of 
the  torpedo  may  be  25  knots  for  a  range  of  200  yards,  or  22  knots  for 
a  range  of  600  yards,  or  intermediate  speeds  for  intermediate  ranges. 
The  charge  is  carried  in  that  portion  of  the  case  near  the  head,  which 
is  fitted  with  an  appaiatus  that  causes  the  explosion  when  the  torpedo 
strikes  the  side  of  a  vessel,  point  first.     Tiie  immersion  of  the  torpedo  is 

*  The  Suhwartzkopf  Whitehead  is  essentially  the  same  astheFiunie  Whitehead, 
but  is  made  of  phosphor  bronze  instead  of  steel. 


The  Whitehead  Torpedo.  227 

regulated  by  horizontal  rudders  at  the  tail,  and  these  are  actuated  l)y 
compressed  air,  governed  by  a  valve,  itself  controlled  by  the  hydro- 
static pressure  due  to  the  itnniersion,  and  by  an  attached  pendulum 
weighing  from  30  lb.  to  40  lb.  The  method  of  regulating  lateral  direc- 
tion is  by  vertical  fins  permanently  adjusted  in  accordance  with  expe- 
riments made  with  each  torpedo.  The  Whitehead  is  ejected  Ijy  com- 
pressed air  or  by  the  explosion  of  a  small  charge  of  gunpowder,  the 
directing  tubes,  carriages,  or  other  apparatus  varying  according  to  the 
conditions  of  each  situation,  such  as  under-water  or  over-water  dis- 
charge, and  front  or  broadside  discharge.  These  torpedoes  can  also  be 
discharged  by  gravity,  like  the  ball  of  a  falling  pendulum,  release 
being  effected  at  or  near  to  the  lowest  point  of  the  fall,  or  by  running 
down  an  inclined  plane  curved  somewhat  in  the  form  of  a  parabola, 
viz.,  steep  at  first,  then  gradually  becoming  nearly  horizontal  as  the 
torpedo  reaches  the  water  surface.  This  latter  method  appears  to  be 
specially  favourable  for  employment  in  shore  batteries.  It  was  tried 
at  sea,  but  discarded  owing  to  the  irregularities  caused  by  the  pitching 
motion  of  vessels  in  a  seaway.  The  defects  of  the  Whitehead  torpedo 
in  the  order  of  their  importance  are  : 

1.  Inefficiency   due    to    the     small    charge     carried,    which    is   now 

insuflicient  to  destroy  the  hulls  of  vessels  like  modern  ironclads 
that  are  divided  into  numerous  water-tight  compartments. 

2.  Uncertainty  as  to  Accuracy. — For,  although  a  vessel  can  generally 

be  hit  up  to  a  range  of  300  yards,  this  cannot  be  depended  upon 
the  course  of  a  Whitehead  occasionally  being  very  erratic, 
especially  with  over-water  discharge  from  the  broadside  of  a 
vessel  at  speed.  Moreover,  during  handling  and  discharge,  the 
fins,  and  rudders,  and  other  gear  projecting  from  the  body  of 
the  torpedo,  are  liable  to  derangement.  Inaccuracy  as  to  sub- 
mersion is  also  encountered,  due  to  imperfections  in  the  design 
or  manufacture  of  the  automatic  controlling  gear. 

3.  F.rpentie. — The  manufacturing  cost  of  one  Whitehead   being  over 

5001.,  to  which  must  be  added  the  siiare  of  price  first  paid  for 
the  patent,  and  the  cost  of  the  discharging  appliances. 

4.  Intricacy. — The  torpedo   containing  a  quantity  of  highly  finished 

and  complicated  machinery. 

5.  Difficulties  in  Manipulation. — Great  intelligence  on  the  part  of 

the  personnel  combined  with  a  long  and  careful  training,  being 
essential. 

6.  Difficulties  in  Maintenance. — Constant  attention  and  care  being 

required  to  keep  the  torpedoes  and  their  impulse  arrangements 
clean  and  efficient. 

q2 


228  Torpedoes. 

7.  Loss   of  Control  after  Discharrje,   which,   combined  with  the  un- 

certainty as  to  accuracy  ah-eady  mentioned,  increases  the  diffi- 
culties attending  the  employment  of  these  torpedoes  in  fleet 
actions. 

8.  Motive  Power  Dangerous,  the  highly  compressed  air  having  some- 

times burst  the  torpedo.  Hostile  shot  would  increase  this 
danger. 

9.  Space  Occupied,   especially  when   tliat   of  the  appurtenances   are 

taken  into  consideration. 

Not  only  are  the  above  defects  recognised  by  many  critics  whose 
opinions  are  not  to  be  despised,  but  the  torpedo  boats  specially  built 
to  carry  the  Whitehead  are  now  regarded  with  much  less  favour  than 
formerly,  owing  to  the  physical  impossibility  that  human  beings  can 
live  on  board  when  the  boats  are  required  to  keep  the  sea  for  any 
length  of  time.  Indeed,  it  appears  that  all  Whitehead  torpedo  boats 
that  are  too  large  to  be  hoisted  on  board  a  man-of-war,  and  yet  too 
small  themselves  to  keep  the  sea,  must  be  relegated  to  harbour  or  river 
defence. 

Contradictory  as  it  may  seem,  defect  No.  3 — the  great  cost  connected 
with  the  Whitehead — has  been  the  means  of  perpetuating  its  employ- 
ment. After  spending  vast  sums  of  public  money  on  any  engine  of 
war,  those  responsible  are  loth  to  acknowledge  its  defects,  and  prefer 
to  spend  more  in  attempting  to  perfect  the  invention.  As  i-egards  the 
Whitehead  we  are  in  the  same  boat  with  most  of  our  neighbours,  and 
we  were  almost  compelled  to  act  as  we  have  done,  but  it  is  high  time 
that  other  inventions  should  be  carefully  examined  and  compared  with  it. 

The  Howell  Torpedo. — This,  the  invention  of  Captain  Howell,  United 
States  Navy,  is  similar  to  the  Whitehead  both  in  outward  appearance 
and  in  general  design.  Fig.  102.  The  charge  is  carried  in  the  forward 
cone,  the  motor  in  the  centre  of  the  body,  twin  screws  and  horizontal 
and  vertical  directing  rudders  aft.  The  most  important  novelty  is  the 
motor,  which  is  simply  a  ponderous  steel  gyroscope  on  a  horizontal 
axis  across  the  centre  of  the  torpedo.     See  Figs.  103  and  10-1. 

A  torpedo  8  ft.  long  and  13.3  in.  in  diameter  carries  70  lb.  of 
explosive,  and  a  flywheel  of  110  lb.,  tlic  whole  torpedo  weigliing  only 
325  lb.  A  Howell  torpedo,  as  heavy  as  the  Whitehead,  and  14  ft.  6  in. 
long,  will  carry  over  20,0  lb.  of  explosive. 

The  flywheel  is  spun  up  to  a  speed  of  10,000  revolutions  per  minute, 
over  half  a  million  of  foot-pounds  being  then  stored  in  the  motor.  A 
Barker's  mill  is  generally  employed  to  perform  this  work,  the  flywheel 
axle  being  grasped  externally  by  a  clutch  on  the  driving  shaft  of  the 
Barker's  mill,  and  lieing  disengaged  when  desired. 


TJie  Howell  Torpedo. 


229 


Tlie  shafts  of  the  twin  screws  are  connected  to  the  flywheel  axle  by 
mitre  wheels,  and  it  is  stated  that  an  8-ft.  torpedo  can  be  driven  by  a 
110  lb.  flywheel  at  a  speed  of  24  knots  for  GOO  yards. 

"  The  fundamental  principle  upon  which  the  stei^rini^  of  the  tor])edo 


is  based  is  that  if  a  revolving  flywheel  be  acted  upon  by  any  force 
which  tends  to  turn  it  about  any  axis  not  parallel  to  its  own,  there  will 
be  a  resultant  motion  about  an  axis  perpendicular  to  the  plane  of  those 
two.  This  ofi"sets  and  opposes  lateral  deflection  of  the  torpedo,  and 
compels  it  to  travel  in  the  course  in  which  it   was  originally  pointed  or 


230 


Toiyedoei' 


launched.  The  axis  of  the  flywheel  being  hoi'izontal,  any  extraneous 
force  tending  to  deflect  it  laterally  will  cause  the  torpedo  to  roll,  which 
rolling  can  be  conveniently  employed  to  bring  into  action  steering 
mechanism  arranged  to  apply  automatically  an  opposite  deflecting  or 
deviating  force  which  will  restore  the  status  quo. 


"  Tlic  steering  mechanism,  Fig.  105,  consists  of  one  or  more  vertical 
rudders  and  rudder-opei-ating  devices,  so  arranged  that  when  the 
torpedo  rolls  to  starboard,  the  helm  automatically  will  be  put  to  star- 
board and   rice  versd.     As  tlio  liorizontal  axis  of  rotation  of   tli(>   fly- 


Thr  Howell  Torpedo.  231 

wluM'l  is  transvorsp  to  tlie  longitiulinal  axis  of  the  torpodo,  it  is  iioccssaiy 
to  provide  a  diving  rudder  to  keep  the  torpedo  during  its  run  at  a 
given  depth.  This  rudder  is  operated  automatically  by  mechanism, 
Figs.  106  and  107,  tlie  action  of  which  is  controlled  by  a  combined 
pendulum  and  regulator,  the  latter  being  governed  by  the  pressure  of 
the  water  which  varies  with  the  immersion  of  the  torpedo.  The  office 
of  the  regulator  is  to  cause  the  torpedo  to  sink  and  maintain  itself 
at  the  required  depth  ;  that  of  the  pendulum  to  prevent  the  torpedo 
from  diving  or  rising  too  abruptly. 

"  At  the  after  end  of  the  torpedo,  surrounding  the  propellers,  arc 
tubes  which,  by  reason  of  the  mass  and  velocity  of  water  flowing 
through  them,  serve  to  stiffen  the  path  against  irregular  movements  in 
the  vertical  plane. 

"  The  discharging  gear  used  up  to  the  present  time  consists  of  a 
frame,  or  derrick,  extending  from  the  ship's  side  under  wliicli  the 
torpedo  is  hung  by  clutches  and  studs  on  its  shell.  Tlie  frame  is 
either  pivotted  on  the  rail  or  fitted  to  slide  in  and  out  on  a 
stationary  beam  ;  in  either  case  the  torpedo  can  be  slung  from  the 
deck,  then  rigged  out  and  operated  with  rods  or  lanyards,  steam  being 
turned  on  the  Barker's  mill,  and  the  wheel  spun  up ;  one  lanyard 
acting  on  a  trigger,  disengages  the  clutch  connecting  the  two  ;  the 
other  lanyard,  acting  also  on  a  trigger  arrangement,  disengages  the 
torpedo  from  the  clutches.  To  give  it  an  impulse  in  the  direction  in 
which  it  is  launched  the  torpedo  is  also  grasped  abreast  tlie  centre  of 
gravity  by  a  downward  switching  clutch,  pivotted  outboard  on  the 
frame  beyond  ;  on  being  detached  from  the  derrick,  it  is  swung  out- 
board in  the  arc  of  a  circle  and  detached  automatically  by  a  check  and 
trigger  on  reaching  the  vertical  below  the  pivot.  This  gives  it  an 
impulse  without  changing  the  angle  of  its  horizontal  axis  with  the 
surface  of  the  water.  The  supporting  frame  is  free  to  swing  below  an 
axis  parallel  to  the  fore  and  aft  line  of  the  torpedo,  so  the  axis  of 
the  ilywheel  is  also  kept  horizontal. 

"  An  improved  apparatiis,  however,  comprises  a  tubulai'  sliicld  jiro- 
tected  by  armour,  in  which  the  torpedo  will  be  placed.  At  the  inner 
end  are  two  cylinders  whose  piston-rods  reach  forward  and  press 
against  studs  on  the  middle  body.  The  tube  and  support  revolve  about 
a  centre  to  allow  lateral  strain,  the  power  for  revolving  the  flywheel 
being  conducted  through  this  centre.  Steam  from  the  Barker's  mill 
exhausts  back  into  the  condenser,  thus  stopping  the  humming  sound, 
to  which  great  objection  had  been  justly  raised.  By  one  action  of  a 
lever  the  power  is  shut  oil'  and  the  torpedo  cjecti'd." — Engineerinfj, 
January  20,  1888. 


232  Torpedoes. 

The  objection  has  been  raised  that  this  torpedo  "does  not  lie  in  a 
state  of  constant  readiness,  but  has  to  be  spun  up  "  before  it  is  ready 
to  launch,  but  it  must  be  noted  that  when  the  wheel  has  been  spun  up, 
very  little  power  will  keep  it  going,  and  therefore  the  torpedo  can  be 
kept  in  the  state  of  "  ready "  from  the  commencement  of  an  action 
until  its  termination,  unless,  in  the  mean  time,  it  be  discharged. 

Remembering  the  defects  of  the  Whitehead  torpedo  which  have 
been  enumerated,  it  will  be  found  that  most  of  them  have  been  over- 
come in  tJie  Howell  torpedo. 

Thus  : 

1.  The  efficiency  duo  to  small  charge  carried  has  been  met. 

2.  Also  the  uncertainty  as  to  accuracy. 

3.  Also  the  great  expense,  for  the  Howell  torpedo  and  its  appurte- 
nances are  cheaper  to  manufacture. 

4.  Also,  simplicity  of  detail  is  substituted  for  tliat  intricacy  and 
delicacy  of  detail  which  in  the  "Whitehead  enlists  our  astonishment 
and  admii'ation. 

T).  As  regards  ,manipulation,  comparative  trials  are  required,  the 
advocates  of  the  new  arm  being  confident  of  the  result. 

G.  The  maintenance  of  the  simpler  apparatus  must  be  less  trouble- 
some and  costly. 

7.  The  new  arm  is  evidently  under  better  self-control  after  discharge. 

8.  The  danger  due  to  the  existence  under  fire  of  a  chamber  full  of 
highly  compressed  air  is  absent. 

9.  And  finally,  the  space  occupied  is  less  than  with  the  White- 
head. 

In  short,  it  would  appear  that  the  Howell  is  superior  on  nearly  all 
points,  and,  on  account  of  its  humming  sound,  is  inferior  only  as  an 
arm  for  a  sneak  boat,  or  for  a  vessel  attempting  to  run  a  blockade. 

The  torpedo  has  been  officially  tried  in  the  United  States,  and  the 
Naval  Board  detailed  to  carry  out  these  experiments  has,  it  is  under- 
stood, reported  very  favourably  on  the  invention. 

If  used  for  harbour  defence  these  torpedoes  might  be  placed  in  shore 
batteries,  and  their  simple  fittings  and  accessories  would  not  be  difiloult 
to  keep  in  order.  But  it  would  generally  be  preferable  to  mount  them 
on  some  floating  body  and  moor  it  under  the  shelter  of  the  land  or  a 
fort  in  a  convenient  place  for  aiding  the  defence.  By  tliese  means,  a 
foe  would  be  kept  in  ignorance  of  the  position  from  wliich  his  vessels 
might  be  torpedoed  should  they  attempt  to  force  a  passage. 


CHAPTER  XXIL 

Controllable  Torpedoes. 

The  next  class  of  torpedo  to  be  considered  is  that  which  is  con- 
trolled after  discharge  and  is  directed  to  its  object  from  the  base  whence 
it  is  launched. 

For  many  years  it  has  been  seen  that  a  successful  weapon  of  this 
nature  would  be  useful  in  certain  situations  for  harbour  or  river 
defence ;  and  its  more  sanguine  admirers  believed  in  its  becoming  an 
important  naval  arm,  but  at  present  the  best-known  forms  of  con- 
trollable torpedo  find  no  favour  in  our  own  or  other  navies. 

The  Lay,  the  Ericcson,  the  Berdan,  the  Sims-Edison,  the  Nordenfelt, 
the  Patrick,  the  Lay-Patrick,  and  the  Brennan  are  those  which  have 
received  the  most  attention. 

The  Berdan  is  propelled  by  the  gas  from  burning  rocket  composition  ; 
the  Lay  and  Patrick  by  compressed  carbonic  acid  gas  ;  the  Ericcson  by 
compressed  air ;  the  Sims-Edison  by  electricity  located  at  the  base ; 
the  Nordenfelt  by  electricity  carried  in  the  torpedo.  Nearly  all  are 
controlled  by  electricity  acting  on  valves  or  on  electric  motors. 

The  Brennan  Torfedo,  however,  is  propelled  and  controlled  without 
gas,  air,  or  electricity,  and  it  carries  but  little  machinery,  for  the  engine 
that  propels  it  is  stationed  at  the  base  of  operations. 

"The  mode  of  propulsion  is  effected  by  the  rapid  unwinding  of  two 
wires  from  two  drums  or  reels  carried  in  the  interior  of  the  torpedo, 
and  connected  respectively  to  the  two  propeller  shafts,  thereby  causing 
the  two  propellers  to  revolve  at  a  high  rate  of  speed,  and  consequently 
forcing  the  torpedo  through  the  water.  The  unwinding  of  these  two  wires 
is  effected  by  means  of  a  powerful  winding  engine  placed  at  the  starting 
point  on  shore.  Considerable  interest  has  been  evinced  in  this  inven- 
tion since  its  first  appearance,  because  of  the  apparent  paradox  in- 
volved in  its  mode  of  propulsion,  in  that  the  harder  this  torpedo  is 
pulled  back  the  faster  it  will  go  ahead  ;  but  on  consideration  it  will 
be  seen  that  by  hauling  in  the  wires  at  a  certain  rate,  a  corresponding 
rate  of  revolution   is  imparted  to  the  drums  which    are  fixed  to  the 


234  Torpedoes. 

propeller  slmfts  in  tho  torpedo,  and  so  to  the  two  propellers,  wliicli 
are  thereby  capable  of  developing  a  certain  horse-power,  and  if  this 
horse-power  be  sufficient  to  overcome  the  retarding  strain  on  tiie 
wires,  and  to  leave  a  margin  of  thrust,  then  the  torpedo  must  be 
propelled  through  the  water ;  and  the  only  limit  to  the  speed  of  the 
torpedo  is  apparently  the  strength  of  the  wires." 

The  principle  involved  is  similar  to  one  embodied  in  a  gun-rammer 
which  Lieutenant  (now  Major)  T.  Englisli,  R.E.,  invented  many  years 
ago,  and  brought  to  the  notice  of  the  Ordnance  Select  Committee.  It 
consisted  of  a  small  carriage  engaging  the  bore  of  a  gun  by  rollers  driven 
by  a  chain  so  that  the  carriage  or  rammer  was  driven  down  the  bore  on 
the  chain  being  pulled  in  the  contrary  direction. 

Some  doubts  have  arisen  as  to  the  accuracy  with  which  the  Brennan 
torpedo  can  be  steered,  but  the  pei-sonal  equation  enters  largely  into 
this  matter,  and  those  who  know  it  best  and  are  well  able  to  judge  of 
its  capabilities  are  satisfied  that  it  is  sufficiently  accurate. 

Although  the  greatest  care  has  been  taken  to  guard  the  secrets  of 
its  construction,  a  very  clever  guess  at  its  main  features  was  publislied 
in  Engineering,  June  and  July,  1887,  whence  the  following  description 
and  the  above  quotation  are  abstracted  by  permission  of  the  editor. 


"  Fig.  108  shows  a  section  of  the  torpedo ;  Fig.  109  is  a  plan  of  the 
torpedo;  Fig.  110  is  a  vertical  section  looking  aft  tliroutrli  X  Y; 
Fig.  Ill  is  a  general  view  of  the  winding  engine;  and  Fig.  llL* 
represents  the  mode  of  using  the  torpedo. 

"  The  dimensions  of  the  present  Brennan  torpedo  are  25  ft.  by  3  ft. 
by  11  ft.  ;  weight,  fully  equipped,  25  cwt.  ;  speed,  about  20  miles  per 
hour  ;  I'ange,  from  1^  to  2  miles. 

"  I.  Mode  of  Propulsion. — In  Fig.  108,  A  and  B  show  the  two  drum.s, 
or  reels,  on  which  is  wound  the  wire  by  the  unwinding  of  which  the 
torpedo  is  caused  to  travel  through  the  water;  the  fore  drum  A  is  attached 
direct  to  the  inner  solid  propeller  shaft  S,  and  the  after  drum  B  is 
fast  on  to  the  outer  hollow  steel  propeller  shaft  S'  ;  these  two  drums, 
liy  tho  unwinding    of   tlie   wire    w  m;',  are   ri'volvod   in    the  sani.'   iliicc- 


J'ig<  108. 


To  face  iniije  234. 


cy — G^ 


The  Breanan  Torpedo.  235 

tion,  and  tlioir  respective  propeller  shafts  also,  up  to  tin;  point  D  ; 
where,  by  a  combination  of  bevel  wheels  (precisely  similar  to  tlie 
arrangement  adopted  in  the  Whitehead,  see  Fig.  II-'j),  tlie  outer 
hollow  shaft  S'  has  its  motion  reversed  for  the  purpose  of  revolving 
the    two    tliree-bladed    propellers    P  P'   in    opposite   directions.       At 


Fig.  111. 
first  sight  this  appears  a  most  unnecessary  complication,  if  it  be 
only  required  to  effect  the  revolution  of  the  two  propellers  in  opposite 
directions,  for  this  work  could  be  more  simply  performed  by  taking  the 
wires  off  the  two  drums,  A  and  B,  in  opposite  ways  ;  but  for  the  purpose  of 
steering,  the  two  propeller  shafts  should  revolve  in  the  same  directioii. 


The  Brennan  Torpedo. 


235 


tion,  and  tlioir  respective  propeller  shafts  also,  up  to  the  point  D  ; 
where,  by  a  combination  of  bevel  wheels  (precisely  similar  to  the 
arrangement  adopted  in  the  Whitehead,  see  Fig.  113),  the  outer 
hollow  shaft  S"  has  its  motion  reversed  for  tlie  purpose  of  revolving 
the    two    three-bladed    propellers    P  P^  in    opposite   directions.       At 


Fuj.  111. 
first  sight  this  appears  a  most  unnecessary  complication,  if  it  be 
only  required  to  effect  the  revolution  of  the  two  propellers  in  opposite 
directions,  for  this  work  could  be  more  simply  performed  by  taking  the 
wires  off  the  two  drums,  A  and  B,  in  opposite  ways  ;  but  for  the  purpose  of 
steering,  the  two  propeller  shafts  should  revolve  in  the  same  diroction, 


236 


Torpedoes. 


while  to  enable  tlie  torpedo  to  maintain  as  straight  a  course  as  possible 
without  utilising  its  rudder,  the  two  propellers  should  be  revolved  in 
opposite  directions,  as  was  found  so  necessary  in  the  case  of  the 
Whitehead.     The  two  wires  iv  iv^,  are  led  from   their  respective  drums 


over  the  two  sheaves  a  a^,  respectively,  through  the  <op  of  the  torpedo 
by  a  hole  miidc  just  large  enough  to  take  the  wires,  but  without  any 
gland.  The  wires  then  pass  through  a  brass  eye  in  the  fair  lead  b 
swivelled   to  tlie  guard  (/.     The  drums  A  and  B  arc  removed   from  the 


The  Brennan  Torpedo. 


237 


torpedo  by  witlulrawing  tlie  inner  propciUcr  shaft  8  and  taking  out 
the  fore  drum  A  througli  a  manhole  in  the  side  of  tlie  torpedo ;  the 
drum  B  being  witlidrawn  from  its  propeller  shaft  and  removed  in  the 
same  way. 

"  II.  Tlir.  Method  of  Steerinff.—  On  the  solid  propelh'r  shaft  S  is  cut  a 
screw  thread,  and  immediately  opposite,  in  the  hollow  shaft  S',  a  slot  is 
cut  longitudinally.  A  nut  or  collar  n  with  an  internal  thread  fits  in 
this  slot,  and  on  the  hollow  shaft.  This  collar  n  is  grooved  on  the 
outside,  and  in  this  groove  work  two  studs  on  the  end  of  a  forked  lever 
I,  Fig.  110  ;  this  forked  lever  I  is  carried  by  a  bracket  711  on  the  side  of 
the  torpedo,  and  is  connected  at  K,  its  other  end,  to  a  second  lever  l\ 
which  is  in  turn  connected  to  the  quadrant  of  the  rudder  shaft  r.  From 
this  it  will  be  seen  that  any  movement  given  in  a  longitudinal  direction 
to  that  part  of  the  forked  lever  I  which  fits  in  the  groove  of  the  nut  71, 
must  transmit  to  the  rudder  7-  a  movement  to  one  side  or  the  other. 
This  longitudinal  movement  of  the  forked  arm  of  the  lever  I  is  eflected 
in  the  following  manner.  So  long  as  the  speeds  of  the  two  propeller 
shafts  S  S'  (which  up  to  the  point  D  revolve  in  the  same  direction)  be 
113 


equal,  the  nut  n  with  its  internal  tliread,  and  the  tiiread  on  tlic  outside 
of  the  solid  shaft  at  0,  which  engage,  will  revolve  round  together  with- 
out any  motion  of  the  nut  n  along  the  shaft  S' ;  but  the  instant  a 
difference  of  speed  is  imparted  to  the  two  shafts  S  S\  then  the  nut  n 
will  be  screwed  along  the  shaft  S'  either  forward  or  aft,  depending  upon 
whether  the  thread  is  a  right  or  left-handed  one,  and  upon  which  of 
the  two  shafts  is  increased  or  decreased  in  speed  as  compared  with  the 
other  one.  Thus  port  or  starboard  helm  can  at  any  moment  be  given 
to  the  torpedo  during  its  run  at  the  will  of  the  officer  directing  it,  by 
altering  the  speed  of  one  of  the  shore  drums. 

"  III.  For  Observing  the  Course. — Several  means  have  boon  tried  to 
enable  the  operator  at  any  moment  to  know  the  course  the  torpedo  may 
take  when  running  below  the  surface,  among  which  may  Vjo  men- 
tioned a  float  attached  by  a  Hue  to  the  back  of  the  torpedo,  and  a  hollow 
mast  with  signal  flag,  but  neither  of  these  methods  hav(!  proved  very 
satisfactory,  the  former  proving  a  very  erratic  indicator,  and  the  latter 
taking  too  much  away  from  the  speed  of  the  torpedo.  It  has  now  been 
found  necessary  to  trust  entirely  to  the  use  of  phosphorus,  or  Holmes' 


238  Torpedoes. 

light  mixture,  both  of  whicli  wlien  brouglit  into  contact  with  water 
emit  flame  and  smoke  in  the  track  of  the  torpedo,  the  former  being 
utilised  for  night,  and  the  latter  for  day,  runs.  In  Fig.  108,  h  shows  the 
case  in  which  this  phosphorus,  or  Holmes'  composition,  is  placed,  and 
which  is  in  connection  with  the  water  during  a  run  by  means  of  the 
hole  /(.',  placed  immediately  above  the  case  h.  The  Brennan  may  be 
steered  from  30  deg.  to  40  deg.  to  port  or  starboard,  but  it  cannot 
be  turned  round. 

"  IV.  Maintenance  of  Depth. — To  steady  the  torpedo  in  a  submerged 
run,  the  two  horizontal  steel  fins  F  F,  Fig.  109,  are  provided.  R  R, 
Fig.  109,  are  two  horizontal  bow  rudders,  which  by  means  of  certain 
automatic  arrangements  are  deflected  up  or  down  according  as  the 
torpedo  reaches  below,  or  rises  above  the  depth  it  is  set  to  run  at. 
Tliese  bow  ruddei-s  effect  the  same  object  in  the  Brennan  that  the 
stern  rudders  do  in  the  celebrated  Whitehead,  and  the  only  diflerence 
between  the  Whitehead  and  Brennan  system  of  effecting  the  upward 
or  downward  motion  is,  that  in  the  former  there  is  an  intermediate 
compressed  air  engine  which  actuates  the  stern  horizontal  rudders,  but 
in  the  latter  the  bow  horizontal  rudders  are  directly  actuated  by  the 
automatic  arrangement,  which  consists  of  a  balance  weight  or  pen- 
dulum, and  a  hydrostatic  valve.  One  form  of  this  valve  is  shown  in 
the  bow  compartment  G,  Fig.  108,  where  also  is  placed  the  balance 
weight.  P  is  a  piston  exposed  to  the  water  on  its  lower  face,  and  s  s 
are  two  springs,  the  tension  of  which  latter  can  be  set  to  equalise  the 
pressure  of  water  on  the  lower  face  of  tlie  piston  P  for  any  particular 
depth  at  which  it  may  be  desired  to  run  the  torpedo.  The  movement 
of  this  piston  up  or  down,  corresponding  to  an  increase  or  decrease 
of  submersion,  is  transferred  by  means  of  a  system  of  levers  L  to 
the  rudders  R  R,  and  causes  them  to  be  deflected  up  or  down,  thus 
bringing  the  torpedo  back  to  its  normal  depth.  The  Brennan  is  arranged 
to  be  run  either  on  the  surface,  or  from  8  ft.  to  10  ft.  below  it. 

"Miscellaneous. — In  the  fore  compartment  G,  besides  the  automatic 
arrangements  just  desci-ibed,  is  placed  an  ordinary  self-registering 
instrument  for  recording  the  course  of  the  torpedo  on  its  run,  as 
regards  its  depth  below  the  surface  at  certain  increments  of  time.  Some 
of  the  records  taken  have  registered  great  variations  in  the  depth,  very 
much  more  so  than  has  ever  been  similarly  registered  by  the  Whitehead 
during  the  course  of  a  run.  This  is  only  to  be  expected,  as  the  longer 
and  heavier  Brennan  would  require  more  time  to  recover  its  proper 
depth  and  pass  over  more  ground  in  doing  so  when  once  displaced.  In 
actual  warfare  tiie  charge  of  200  lb.  of  gun-cotton  would  be  placed  in 
this  fore   compartment.     G  G'  are  two  steel  fixed    guards  to  prevent 


The  Brennan  Torpedo.  239 

till!  vertical  stem  nulders  and  tlui  pi-opellcrs  from  liciiig  t'oulod  during 
a  run  of  the  torpedo  by  hawsers,  chain  cables,  nets,  ttc. 

"  V.  The  Wire. — The  steel  wire  principally  used  for  tiic  propulsion 
of  the  Brennan  torpedo,  is  No.  18  W.G.,  l)reaking  strain  G  cwt.  to 
7  cwt.,  weight  per  mile  33  lb.  For  any  length  of  run  three  times  the 
amount  of  wire  is  required  to  be  wound  on  each  drum  ;  thus  for  a  two- 
mile  run,  six  miles  of  wire  for  each  drum  is  needed,  or  twelve  miles  in 
all,  equal  to  a  weight  of  392  lb.,  or  196  lb.  of  wire  per  drum. 

"  VI.  Operation  of  Winding. — The  various  operations  for  winding 
the  wires  on  the  drums  of  the  Brennan  torpedo  are  as  follows  : 

"  1.  The  wire  is  first  wound  oft' the  reel  on  which  it  is  supplied  by  the 
makers  on  to  a  split  drum,  i.e.,  a  reel  or  drum  constructed  to  allow  of 
the  barrel  being  removed  after  the  drum  has  been  filled  with  the  wire. 

"  2.  This  coil  of  wire  thus  formed,  having  a  hollow  core,  is  placed  in  a 
tank  of  lime  water,  and  carefully  rinsed.  If  it  be  not  required  for 
immediate  use  it  is  left  in  this  tank  for  several  hours,  so  as  to  maintain 
the  wire  in  a  good  state  of  preservation. 

"  3.  The  coil  of  wire  is  removed  from  the  lime-water  tank  and  the 
wire  wound  on  to  a  wooden  swift — that  is,  a  reel  in  the  form  of  a  cone 
placed  on  its  base. 

"4.  From  this  wooden  swift  the  wire  is  wound  on  an  ordinary 
drum,  in  a  state  of  tension,  preparatory  to  its  final  winding. 

"  5.  Lastly,  it  is  wound  off  this  ordinary  reel  to  the  torpedo  drum. 
In  this  operation  every  care  must  be  taken  to  insure  the  turns  lying 
close  together-,  so  that  the  riding  turns  may  not  jam  between  any  two 
of  the  underneath  turns ;  and  to  lessen  the  chance  of  such  a  mishap, 
melted  parafin  wax  is  poured  into  every  opening. 

"On  starting  the  winding  of  the  wire  in  this  final  operation,  the  lead- 
ing end  is  passed  through  a  hole  in  one  of  tlie  end  plates,  and  fastened 
there  ;  but  on  the  winding  being  completed  this  end  is  cut  free,  with  a 
view  to  prevent  the  wire  bringing  up  suddenly  on  the  whole  length  of 
it  being  run  out.  In  such  a  case  the  wire  is  pulled  out  of  the  torpedo 
altogether.  If  for  any  reason  the  torpedo  is  stopped  before  the  whole 
length  of  the  wires  has  been  run  out,  the  wires  must  then  be  cut,  and 
the  four  parts  returned  to  the  maker  for  rejointing  up. 

"  VII.  27ie  Winding  Engine  (Fig.  1 11). — The  drums,  3  ft.  in  diameter, 
are  driven  by  a  pair  of  direct-acting  high-pressure  engines,  running  at 
a  great  speed.  Each  cylinder  is  cast  with  the  column  under  it,  the 
latter  being  very  strong  and  of  such  a  form  as  to  inclose  the  main 
woi-king  parts  of  the  engine,  and  to  prevent  the  wires  from  becoming 
entangled  with  any  part  of  the  engines  in  the  event  of  the  wire  breaking. 
The  steam  is  admitted  by  means  of  a  valve  common  to  both  engines, 


240  Torpedoes. 

and  a  governor  is  provided.  The  drums,  running  loose  on  the  shafting, 
are  connected  by  a  'jack-in-tlie-box'  arrangement,  by  which  their  respec- 
tive speeds  can  be  regulated  by  means  of  a  foot-brake  without  altering 
the  speed  of  the  engines.  This  'jack-in-the-box  '  is  arranged  as  follows  : 
Cast  solid  on  or  bolted  to  each  drum  is  a  mitre  wheel,  and  connecting 
these  two  mitre  wheels  are  two  smaller  ones,  revolving  on  tlieir  own 
centres,  fixed  on  a  carrier  which  is  keyed  to  the  main  shaft.  As  soon 
as  the  main  engine  starts,  the  two  small  mitre  wheels,  which  ai-e  in  one 
with  the  shaft,  are  revolved  with  it,  and  carry  round  with  them  the 
two  larger  mitre  wheels  and  consequently  the  drums.  Hence  it  will 
be  seen  that  on  the  brake  being  applied  to  one  of  tlie  drums,  the 
small  mitre  wheels  will  revolve  round  their  own  centres,  the  effect  of 
which  is  to  increase  the  speed  of  the  other  drum.  As  the  speed  of 
the  one  decreases  so  the  other  increases.  The  columns  are  braced 
together  under  the  cylinders  by  another  casting,  and  the  whole  stands 
upon  a  cast-iron  sole-plate,  thus  making  a  very  rigid  formation.  The 
engine  is  capable  of  working  up  to  100  indicated  horse-power. 

"VIII.  The  Operation  of  Running. — The  torpedo  is  placed  on  a 
launching  carriage,  constructed  in  such  a  manner  that  the  torpedo 
is  automatically  set  free,  and  launched  or  pitched  clear  of  it  into  the 
water,  on  the  carriage  reaching  the  desired  position  on  the  line  of  rails, 
laid  on  an  incline  to  the  water's  edge.  The  hydrostatic  valve  is  then 
set  so  that  the  horizontal  bow  rudders  are  correctly  regulated,  de- 
flection upwards,  for  the  particular  depth  and  speed  it  is  intended  to 
run  the  torpedo  at,  the  speed  being  governed  by  the  number  of  revolu- 
tions given  to  the  winding-in  drums.  The  shore  ends  of  the  two 
wires  are  taken  from  the  torpedo,  secured  to  the  winding  drums,  and 
one  or  two  turns  of  the  wires  wound  on.  The  carriage  with  the 
torpedo  is  then  run  down  the  incline,  and  the  latter  launched  auto- 
matically into  the  water,  the  winding  engine  being  at  the  same  instant 
started.  The  torpedo  then  runs  the  required  course  and  is  guided 
by  the  movement  of  the  stern  vertical  rudders  to  port  or  starboard. 
Its  course  is  indicated  to  the  observer  on  shore  by  the  smoke  in 
day  runs,  and  in  night  runs  by  the  light  emitted  from  the  composition 
in  the  case  h  (see  Fig.  108). 

"In  the  sketch  Fig.  112,  the  windhig  engine  is  shown  in  a  subter- 
ranean gallery  in  the  fort  F,  with  the  line  of  rails  laid  to  a  point 
well  beyond  low-water  mark.  E  is  the  engine,  T  a  torpedo  on  its 
carriage  ready  for  launching,  T'  a  torpedo  running  its  course  towards 
tlic  enemy's  ship  attempting  to  pass  tliis  earthwork. 

"  This  completes  the  description  of  the  Brennan  torpedo  and  its 
tnodas  operandi,  and   it  will   be  evident  to  every  one  versed  in  tor- 


The  Brennan  Torpedo.  241 

pedo  matters  that  mucli  of  tlie  success  of  this  torpedo  as  regai'ds 
three  most  important  points,  viz.,  "  speed,"  "  maintenance  of  doptii," 
and  "  straightness  of  run,"  is  by  no  means  due  to  any  special  features 
in  the  original  invention,  but  rather  to  the  fact  of  its  having  been 
perfected  at  Chatham  under  the  fostering  care  of  scientific  otEcers  who 
are  intimately  acquainted  with  the  details  of  the  Whiteliead  torpedo 
with  all  its  wondei-ful  and  clever  mechanism. 

"  1.  Speed. — Tlie  high  speed  of  the  Chatham-Brennan  is  due  not 
alone  to  the  clever  mode  of  its  propulsion,  but  in  a  great  measure  to 
the  form  and  shape  of  its  hull,  and  to  the  perfection  of  the  winding 
engine  ;  the  former  has  been  proved  by  Mr.  Froude  to  be  the  most 
suitable  form  for  obtaining  high  speeds  for  totally  submerged  vessels 
(it  would  be  adopted  for  the  Whitehead  were  it  not  for  the  necessity 
of  a  cylindrical  compressed  air  chamber) ;  the  latter  (the  engine) 
has  been  specially  designed  at  Chatham,  and  constructed  by  Messrs. 
Yarrow  and  Co. 

"  2.  Straiglitness  of  Run. — Two  screws  revolving  in  opposite  direc- 
tions by  which  a  wholly  submerged  vessel  is  more  capable  of  maintain- 
ing by  itself  a  straight  course  belongs  to  the  Whitehead  invention,  as 
also  does  the  system  of  gearing  (shown  at  D,  Fig.  108),  l)y  whieli  this 
effect  is  obtained. 

"  3.  Maintenance  of  Dejith.  —  Horizontal  bow  rudders  worked  auto- 
matically by  a  hydrostatic  valve  and  balance  weight,  together  with 
fixed  horizontal  after  fins,  by  the  combination  of  which  a  wholly  sub- 
merged vessel  may  be  maintained  during  its  run  at  a  fairly  constant 
depth,  is  also  an  adaptation  from  the  Whitehead  invention. 

"4.  The  Secret. — Evidently  the  great  and  only  secret  in  connection 
with  the  Brennan  was  the  fact  of  its  having  been  patented  ;  a  secret 
which  has  apparently  been  very  well  kept." — Engineering,  1887. 

5.  C/teapness  of  Construction  is  claimed  by  the  advocates  of  the 
Brennan  as  one  of  its  advantages,  but  a  100  I.H.P.  steam  engine  is  a 
costly  item,  and  it  can  only  operate  one  torpedo  at  one  time,  after 
which  a  period  of  preparation  must  elapse  before  a  second  torpedo  can 
be  discharged.  Moreover  the  bomb-proof  engine  room,  and  the  covered 
gallery  to  the  water's  edge,  are  costly  ;  and  if  the  torpedo  itself  Ije  cheap 
to  manufacture  the  right  to  do  so  was  certainly  dear  to  buy.  On  the 
whole,  the  advocates  of  this  torpedo  are  scarcely  justified  in  posing  as 
economists. 

6.  Range  of  Effective  Action. — Its  range  is  said  to  be  about  3000 
yards,  but  it  must  be  impossible  to  insure  a  strike  at  this  distance 
except  under  the  most  favourable  circumstances  of  weather,  light,  A-c.  ; 
and  then  only  if  the  operator  be  situated  at  a  considerable  elevation 

R 


242  Torpedoes. 

above  the  water  level.  The  engine  should,  however,  be  near  to  the 
launching  way,  and  many  difficulties  are  encountered  when  the  operator 
is  removed  to  a  distance.  The  range  of  3000  yards  is  often  vaunted 
as  a  grand  affair,  whereas  in  reality  the  greatest  objection  to  the 
Brennan  is  its  limited  sphere  of  action  caused  by  the  necessity  of 
working  it  from  a  fixed  point. 

7.  lite  Wires  are  easily  broken  by  a  kink  or  sudden  jerk,  but  the 
history  of  the  torpedo  certainly  proves  that  its  success  is  principally  due 
to  the  clever  manner  in  which  the  wires  have  been  pulled. 


243 


CHAPTER  XXII  r. 
Torpedo    A  r  t  i  l  l  p:  r  y. 

The  idea  of  projecting  torpedoes  to  a  distance  by  means  of  artillery 
is  old,  and  a  proposal  to  employ  mortars  for  this  purpose  was  brought 
forward  officially  in  this  country  some  years  ago,  but  experiments  were 
not  recommended, '  high  angle  fire  from  mortars  being  considered  too 
inaccurate  for  the  purpose. 

The  correctness  of  this  view  may  be  open  to  doubt,  modern  rifled 
mortars  giving  very  accurate  results.  The  other  great  difficulties  of 
the  problem  probably  afforded  the  real  reason  for  refusing  to  carry  out 
any  experiments  in  this  direction. 

The  subject  has,  however,  received  the  attention  it  deserves  in 
America.  Mr.  MefFord,  a  schoolmaster  of  Ohio,  was  the  pioneer.  In 
1883  he  designed  and  constructed  an  air  gun  for  throwing  dynamite 
charged  shells.  It  was  28  ft.  long,  2  in.  bore,  \  in.  thick,  with  an  air 
reservoir  of  1 2  cubic  feet  capacity,  carrying  500  lb.  pressure.  Lieutenant 
(now  Captain)  E.  L.  Zalinski,  United  States  Artillery,  took  up  the 
invention,  and  has  worked  at  it  ever  since  with  great  skill  and  per- 
sistency. In  this  he  has  been  backed  by  a  strong  financial  company, 
and  has  been  assisted  by  several  high  State  officials,  including  the 
Secretary  of  the  Navy. 

An  arm  of  great  power  and  accuracy  has  been  dovclopiid,  the  result 
being  a  complete  vindication  of  the  theories  held  by  the  advocates  of  air 
propulsion  for  torpedo  artillery.  The  ballistic  properties  of  the  air  gun 
are  not  sufficiently  appreciated  by  many.  In  the  first  place,  owing  to 
the  size  of  the  air  reservoir,  the  pressure  exerted  on  the  base  of  the 
projectile  is  nearly  constant  throughout  the  entire  length  of  the  bore  ; 
very  different  from  the  powder  gun,  wherein  the  pressure  falls  rapidly 
from  the  breech  to  the  muzzle.  Thus,  in  a  powder  gun  of  16  calibres, 
the  initial  pressure  being,  say,  40,000  lb.  per  square  inch,  the  mean 
available  pressure  may  be  under  12,000  lb.  But  in  an  air  gun  the 
length  would  be,  say,  120  calibres,  or  nearly  7.5  times  16,  and  if 
2000  lb.  were  used  in  a  reservoir  having  ten  times  the  capacity  of  the 
bore,  the  mean  pressure  would  be  1900  lb.,  which,  nuiltipli(Ml  by  7.5, 
K  2 


244  Torpedoes. 

would   be  equivalent   to  11,250  lb.    acting  throu.^li   tlie   sami  length  as 
the  powder  gun. 

In  the  second  place,  owing  to  the  absolute  certainty  with  which 
the  air  pressure  can  be  regulated  to  any  desired  pressure,  and  to  the 
uncertainty  as  to  the  pre.ssure  produced  by  the  explosion  of  a  gun- 
powder charge,  the  former  is  evidently  much  better  adapted  than  the 
latter  for  discharging  projectiles  filled  with  detonating  compounds. 
It  is  well  known  that  occasionally,  if  rarely,  exceedingly  high  and 
abnormal  pressures  have  boon  recorded  in  experiments  with  heavy 
ordnance,  no  satisfactory  explanation  having  ever  been  propounded 
except  that  of  so-called  "  wave  action."  The  possibility  of  such  action 
makes  a  powder  gun  unsuitable  for  torpedo  artillery.  Again,  the 
accurate  manner  in  which  range  can  be  altered  with  the  air  gun  by  alter- 
ing pressure  instead  of  elevation  is  an  important  factor  in  its  favour. 

On  the  whole,  therefore,  Captain  Zalinski  may  be  considered  to  act 
wisely  in  adhering  to  air  propulsion  as  the  best  method  of  solving  the 
difficult  problem  on  which  he  is  engaged ;  and  this,  although  the  air 
gun  possesses  a  great  disadvantage  in  its  length,  and  the  space  it 
necessarily  occupies  wherever  its  emplacement  may  be  located. 

Experience  with  the  2-in.  gun  already  mentioned  indicated  that  : — 
"1.  The  valve  should  be  automatic  in  its  action  as  to  opening  and 
closing,  and  should  permit  the  escape  of  a  uniform  volume  of 
air  between  the  two  events. 
"  2.  The  length  of  gun  should  be  as  great  as   can  be  readily   mani- 
pulated. 
"  3.   Tiie  pressure  should  be  at  least  1000  lb. 
"  4.  The  gun  should  be  easily  trained." 

A  4-in.  gun  was  next  manufactured,  and  many  interesting  experi- 
ments made  whereby  the  fuzes  and  ammunition  were  impro\  ed. 

In  1885  an  8-in.  gun  was  mounted  at  Fort  Lafayette.  It  consists 
of  four  lengths  of  f  in.  wrought-iron  tubing  rivetted  together  and  lined 
with  -|-in.  seamless  brass  tubing.  The  barrel  is  supported  on  a  braced 
truss.  The  breech  is  closed  by  a  door  opening  inwards  to  the  side  of 
the  valve,  and  the  whole  revolves  round  two  trunnions  projecting  from 
a  cast-iron  breech-piece.  The  trunnions  are  carried  on  a  cast-iron 
standard  resting  on  a  chassis  resembling  that  in  general  use  for  heavy 
guns.  Two  cylinders  are  carried  on  the  chassis ;  one  operates  the 
traversing  gear,  the  other  the  elevating  gear.  The  liand  lever  of  the 
firing  valve  is  so  placed  that  No.  1  of  the  gun  can  both  aim  and  tire  it ; 
the  elevating  gear  is  also  under  his  control,  and  the  pressure  gauge 
under  his  observation.  In  short,  the  entire  mechanism  is  under  the 
direct  conti'ol  of  one  man. 


ZaUnskl's  Tori>nh>  ArtUlery. 


245 


246  Torpedoes. 

The  air  reservoir  has  a  capacity  of  137  cubic  feet,  and  is  composed 
of  wrought-iron  tubes  about  1  ft.  in  diameter,  wliich,  in  this  experi- 
mental piece,  rested  on  tlie  cliassis.  When,  however,  these  guns  are 
mounted  in  emplacement  tlie  air  reservoir  is  placed  separately  and 
thoroughly  protected.  The  gun  and  carriage  are  also  hidden  in  a  pit, 
the  rear  half  of  which  can  generally  be  protected  by  a  splinter-proof 
covering,  a  traversing  range  of  180  deg.  being  sufficient  in  most 
positions. 

The  8-in.  gun  lias  sent  shells  containing  GO  \h.  of  exjjlosive  to  ranges 
of  2\  miles,  and  100-lb.  shells  up  to  3000  yards;  10^  in.,  12J  in.,  and 
15  in.  guns  have  been  manufactured,  and  they  are  intended  to  throw 
shells  containing  charges  of  2001b.,  400  lb.,  and  600  lb.  respectively,  to 
ranges  approacliing  two  miles,  with  pressures  not  exceeding  1000  lb. 
Fig.  114  sliows  a  15-in.  gun  of  recent  manufacture.  The  entire  arrange- 
ment rotates  round  a  fixed  vertical  cone  inside  which  the  air  connections 
are  formed  to  the  pipes  leading  to  the  reservoir.  These  guns  are  made  of 
bronze,  and  are  40  ft.  long,  but  Captain  Zalinski  states  tliat  tlie  bore 
can  be  reduced  in  length  if  necessary.  The  thickness  of  the  tubes 
forming  the  bore  need  not  exceed  |  in.,  but  it  is  generally  somewhat 
thicker  in  order  to  obtain  rigidity.  When  weight  is  important,  the 
tubes  can  be  very  lightly  constructed,  especially  if  fixed  at  a  con- 
stant angle,  which  can  be  done  in  a  torpedo  boat.  When  several  of 
these  guns  are  employed  in  battery  (as  in  the  United  States  war  vessel 
under  construction,  which  carries  three  guns),  a  large  central  air  reser- 
voir can  be  provided  in  addition  to  the  one  serving  each  gun.  The 
central  reservoir  can  be  kept  at  nearly  double  the  normal  pressure, 
a  supply  cock  provided  to  each  gun  reservoir  being  so  constructed  that 
it  opens  automatically  when  the  firing  valve  closes.  Thus,  the  rapidity 
of  fire  is  governed  by  the  speed  with  which  the  projectiles  can  be 
inserted  in  the  bore,  and  nearly  one  round  per  minute  has  been 
obtained. 

The  Ammunition. — As  the  present  pattern  gun  is  a  smooth  bore, 
and  the  maximum  pressure  applied  small,  the  shell  has  thin  walls,  and 
a  wooden  tail  like  a  rocket  stick  provided  with  spiral  ^anes  serves  to 
steady  it  during  flight. 

The  shell  is  charged  with  an  inner  core  of  dynamite  or  similar  high 
explosive,  surrounded  by  asbestos  paper,  and  this  by  an  annular  charge 
of  nitro-gelatine  separated  from  the  shell  wall  by  asbestos.  The  front 
of  the  shell  is  filled  with  camphorated  nitro-gelatine  and  a  pad  of  elastic 
material.  The  shell  usually  carries  three  distinct  voltaic  (silver  chloride) 
batteries,  two  of  which  are  wet  and  one  dry.  The  former  come  into  action 
when  the  shell  strikcssome  haixl  object  that  collapses  the  front,  thus  closing 


Z<iJltisl-l's  Torprdo  Artillery. 


!47 


the  electi'ic  circuit.  If  the  sliell  fall  into  water,  and  the  fiont  be  not 
collapsed,  the  dry  battery  explodes  as  soon  as  the  water  has  wetted  it. 
It  is  stated  that  this  action  can  be  delayed  as  desired,  so  as  to  insure 
any  suitable  submersion  before  the  shell  is  exploded  as  a  torpedo.  A 
somewhat  complicated  arrangement  is  provided  for  automatically  pre- 
venting the  premature  explosion  of  a  shell  when  in  the  bore  of  a  gun  ; 
but  premature  explosion  just  outside  the  gun  is  not  prevented  by  it, 
and  this,  if  it  occcurred,  would  be  nearly  as  disastrous.  Electric 
and  percussion  fuzes  are  also  fired  by  the  automatic  withdrawal 
of  the  tail,  which  is  arranged  to   unscrew   from  the   projectile   when 


\C 
Fvj.  115. 
it  falls  into  the  water.  Experiments  in  America  indicate  that  shells 
fired  against  armour  plates  cause  less  damage  when  exploded  by  percus- 
sion fuzes  than  when  exploded  by  electric  fuzes  placed  in  the  rear  of  the 
projectile.  Asmall  chloride  of  silver  battery  is  carried  in  case  A,  Fig.  115. 
B  is  a  metal  plunger  in  the  vulcanite  cylinder  a  a ;  the  springs  b  b  are 
connected  with  one  pole  of  the  fuze  c,  the  other  going  to  the  metal 
case  A.  When  the  gun  is  fired  the  inertia  of  the  battery  box  causes 
the  ears  e  e  to  be  shorn  off,  and  the  box  takes  a  position  such  that  B 
can  close  the  circuit  when  it  moves  towards  the  battery.  This  occurs 
as  soon  as  the  shell  strikes  an  oVgect.     Captain   Zalinski   has  perfected 


248 


Torpedoes, 


numerous  modifications,  and  has  lately  patented  some  of  them   in  this 
country  (vide  Patent  8995,  June  19,  1888,  on  which  date  he  also   took 


out  a  iiiMic  couiplcto  specification  in   the   United  States,  No.    n84,GG-2). 
Tliose  wlio  wish  to  examine  tlie   matter   minutely   lan   purciiase   those 


Zalim^Jci's  Torpr<lo  Artillrry.  249 

ilocunipnts  for  a  few  p«nce,  but  it  would  occupy  too  iiiucli  space  to 
reproduce  them  on  these  pages. 

Among  other  things  Captain  Zalinski  describes  a  magneto-electric 
arrangement,  to  be  carried  by  a  projectile,  and  to  be  actuated  by 
sudden  motions  caused  by  its  own  inertia,  and  by  changes  in  the 
velocity  of  the  projectile.  IVIany  of  the  details  are  applical)le  to  powder 
guns. 

Accuracy  of  Fire. — The  accuracy  obtainable  from  this  artillery  is 
remarkable.  In  June,  1886,  at  a  trial  before  the  United  States  Naval 
Board,  "  four  out  of  five  shells  landed  in  essentially  the  same  spot  at  a 
range  of  1613  yards,"  and  the  fifth  "went  about  seven  yards  beyond." 
On  the  20th  September,  1887,  the  schooner  Silliman  was  destroyed  at 
a  range  of  1864  yai-ds  (see  1  to  6,  Fig.  116).  After  two  sighting  shots 
with  blind  shell,  the  third  was  loaded  with  55  lb.  of  nitro-glycerine,  and 
severely  damaged  the  target  vessel  (see  2).  The  second  shot  destroyed 
her  (see  3).  The  next  struck  the  wreckage  and  exploded  on  the  sur- 
face (see  4).   The  last  shot  exploded  at  a  small  submersion  (see  6). 

Accuracy  from  a  fixed  platform  on  land  is  therefore  established,  and 
on  a  floating  platform  the  inaccuracy  caused  by  movement  is  much  less 
than  with  powder  guns.  Thus,  with  15  min.  error  in  eleA\ation  an  error 
of  230  yards  at  one  mile  range  would  be  occasioned  in  an  8-in.  rifled 
gun,  whereas  an  error  of  only  15  yards  would  be  met  with  in  the  air 
gun. 

Comparison  loith  Locomotive  Torpedoes. — Torpedo  artillery — as  de- 
veloped in  the  air  gun — compares  favourably  with  other  methods  of 
carrying  a  torpedo  to  any  given  object  of  attack. 

Compared  with  the  Brennan  torpedo  : — 

1.  It  is  not  stopped  by  booms  or  netting. 

2.  Its  speed  is  fourteen  times  as  great. 

3.  It  can  discharge  torpedoes  at  the  rate  of  about  one  per  minute. 

4.  It  has  no  long  life  artery  of  wires  exposed  to  injury. 

5.  Good  practice  can  be  made  when  the  object  attacked  is  enveloped 
in  smoke,  a  mast  being  all  sufficient  to  aim  at. 

6.  It  can  be  used  in  thick  weather,  fog,  and  darkness  (some  portion 
of  the  object  being  visible)  much  better  tlian  an  arm  which  must  be 
kept  in  sight  and  guided  during  the  who'e  run. 

7.  It  can  be  used  effectively  at  short  ranges  from  a  rapidly  moving 
platform,  such  as  a  man-of-war  or  a  torpedo  boat. 

In  these  seven  particulars  the  Brennan  torpedo  is  distinctly  inferior, 
and  its  superiority  on  any  other  point  has  not  been  suggested.  Torpedo 
artillery  has  been  developed  by  Zalinski  to  a  high  state  of  perfection, 
and  the  time  has  arrived  to  stop  any  further  expenditure  on  any   form 


250  Torpedoes. 

of  controlled  locomotive  torpedoes  ;  for  no  system  of  the  kind  can  com- 
pete with  one  that  hurls  large  torpedoes  with  remarkable  accuracy  and 
considerable  range  at  the  rate  of  nearly  one  per  minute  per  gun. 

When  used  at  long  range,  a  fixed  platform  and  a  good  range  finder 
are  essential  for  producing  the  best  results.  We  possess  the  range  finder, 
and  we  ought  to  have  the  gun. 

There  is  but  little  difficulty  in  so  locating  and  directing  torpedo 
artillery  that  the  shells  shall  not  damage  the  mine  defences,  but  loco- 
motive torpedoes  cannot  always  be  employed  over  waters  mined  with 
electro-contact  and  automatic  arrangements  which  are  near  to  tlie 
surface  at  low  water,  especially  in  situations  where  there  is  a  consider- 
able tidal  range. 

Torpedo  guns  are  allied  to  the  artillery  of  the  defence,  and  their 
sphere  of  action  is  similar.  They  should  be  manned  by  gunners  and 
be  directed  by  artillery  officers. 

But  submarine  mines  should  never  be  replaced  by  torpedo  artillery 
or  by  locomotive  torpedoes ;  for,  however  perfect  the  latter  may  be, 
they  do  not  possess  the  blocking  efl'ect  of  hidden  and  unknown  mines. 


INDEX. 


PAGES 

Abbot  (General,  U.S.A.),  frequently  (see  Table  of  Contents) 

Abel  (Sir  Frederick,  C.B.,  &c.),  Gun-Cotton 41,47,49 

Abel  (Sir  Frederick,  C.B.,  &c.),  Circuit-Closer 122 

Abel  (Sir  Frederick,  C.B.,  &c.),  Fuze,  Electric 110 

Abbey  (F.R.S.,  Captain  R.E.,  &c.) 13 

Advanced  Mines 170 

Air  Space  in  Mmes 32,  55 

American  Fuze 112 

Armouring,  Cable  Electric 104 

Armstrong  (Lieut. -Colonel  R.E.)  Relay 121 

Apparatus,  Signalling  and  Firing 134 

Apparatus,  Fuze-indicating          ........  136-140 

Attack  in  Mined  Waters 209 

Atlas  Powder 43 

Automatic  Mines 203 

Barge  for  Cables  (Day,  Summers,  and  Co.)  .         ......         165 

Beardslee's  Fuze 110 

Berdan  Torpedo 233 

Boat  Mines ^221 

Boats  and  Steamers 187-189 

Bombardment,  Mines  to  Prevent 170 

Booms 221 

Boxes,  Connecting  and  Junction 106,  107,  131 

Brennan  Torpedo 233-242 

Brown  (Mr.  E.  0.),  Gun-Cotton 47 

Brown,  Three  Coil  Galvanometer 156 

Browne's  Compound  Fuze 117 

Brugere  Powder 42 

Bucknill  (J.  T.,  Lieut. -Colonel),  frequently  (see  Table  of  Contents) 

Burgoyne  (Field-Marshal  Sir. lohn,  G.C.B.,  &c.) 177 

Cables,  Electric 101  et  seq. 

Carlskrona  Experiments 6 

Cases,  Size  of,  &c 67,  83,  85 

Chain,  Tripping,  &c.  99 

Charge  to  Resist  Countermining  .  223 

Charges,  Electro-contact  !Mines   .........  56 

Chemical  Automatic  Mines 204 

Cherbourg,  Mme  Defence  for       .........         170 

Circuit-Closers      ....  58,  223 

Classification  of  Mines 55 

Coaling  Stations 184 


252 


Index. 


Coast  Towns         .         .         .         . 
Command,  for  Depression  Firing 
Connecting  Boxes 
Connecting  Up  Mines  . 
Connector,  Multiple      . 
Controllable  Torpedoes 
Countermining     . 
Creepuig  for  Cables 
Cribs  of  Timber   . 
Crowning  Cables . 


Danish  and  Swedish  Experiments 

Day,  Summers,  and  Co.,  Barge,  Cable 

Day,  Summers,  and  Co.,  Boats  and  Steamers 

Day,  Summers,  and  Co.,  Mine  Cases,  &c 

Day,  Summers,  and  Co.,  Electric  Light  Carriage 

Defence  of  Mined  Waters    . 

Depot  for  Stores 

Depression  Instruments,  Theory 

Depression  Instruments,  Error 

Designolle  Powder 

Designs  for  Mine  Defence    . 

Detonators  .... 

Disconnecting  Arrangements,  Electro-Contact  M 

Disconnecting  Fuzes    . 

Disconnector,  Single    . 

Disconnector,  IMultiple 

Dormant  Mines   . 

Double  Observation  Firing  . 

Dualin  .... 

]1ynamite     .... 

Dynamometers     . 

Eckermann's  Crusher  Gauges 

Eckermann's  Torpedo 

Electric  Automatic  ISIines    . 

Electric  Light  Arrangements 

Electric  Powder    . 

Electrical  Arrangements  on  Mine  Field 

Electrical  Arrangements  on  Shore 

Embarking  Mines 

English  (T.  Major,  R.E.)  Theory 

English  Gun  Rammer . 

English  Experiments  . 

English  Service  Fuze   . 

Envelope,  Mine  Case,  Theory 

Explosive  Link    .... 

Explosives,  Detonated  Wet 

Explosives,  Effects  of  Freezing    . 

Explosives,  Compared. 

Fergusson  .... 

Firing  Battery     .... 

Firing  Battery,  Coils  for  Testing 

Firing  by  Observation 

Firing  by  Observation,  One  Observer 

Firing  by  Depression   . 

Firing  by  Observation,  Two  Observer 

Fisher  (J.  A.,  Capt.,  R.N.)  Fuze 

Forcite         ..... 

Foreign  Experiments  . 

FormuLf      ..... 


PAOES 

185 
145 
106 
192 
130 
233 
211 
211 
224 
105 


165 
187 

87 
214 
209 
163 
143 
144 

42 
168-192 
,111-113 
128 
116 
129 
130 
173 
145 

41 
41,  46 
14-22 

16,  17 
233 

207 

.213-218 

42 

119-131 

131-151 

193 

13,  24,  33 

234 

4-7  &c. 

113 

23 

75 

33 

33 

41 


,132 


169 
,133 
155 
141 
142 
.14:},144 
145- 153 
HI 
44,  51 
4-7 
(see  separate  list) 


Index. 


253 


Hercules  Powder 
Hooper's  Core 
Howell  Torpedo  . 


PAGES 

•208 

10 

205 

67-69 

I 

lOitll") 

117 

117 


Frame  Torpedoes 
French  System,  Ground  Mines    . 
Frictional  Automatic  Mines 
Froude's  Formute 

Fulton 

Fuzes,  Electric,  Theory 
Fuzes,  Electric,  Sensitive    . 
Fuzes,  Electric,  Requirements    . 

Galvanometers,  hcp.  Instruments  : 
Gauges,  Pressure 
Gelatine,  Blasting 

Gelatine,  Explosive '^f^f 

Gelatine,  Dynamite     ...  *■*•''"* 

Gelignite 

Giant  Powder  .  .  .  ■ 
Ground  M-ines  .... 
Gun-Cotton 


13  et  srq. 

.    43,  50 

4249 


44 
42 

10,  78,  79 
.     41-47 


42 

104 

228,  232 


Instruments 
Insulation  Test    . 
Insulator,  Cable  Electric 


Lay,  Torpedo 
Laying  Mines,  &c. 
Lefroy  (General  R.A., 
Lithofracteur 
Lucigen  Lights    . 


&c.) 


161 
104 


55 
50 

.  Preface 
160 


Jackets,  Wooden  and  Cork 

Jekyll  (Major  R.E.,  CM. G.)       .         .         •        ;         ■ 
Jervois  (General  8ir  Wm.  F.  Drummoml,  k.C.B.,  &c. )      . 

Johnson,  Megohm  Resistance ^"^ 

Judson's  Powders inr>Tj'i 

Junction  Boxes lUb-iai 

King  (Colonel  U.S.  Army) 


13 

233 

191-194 

169 

41 

219 


Macinlay      ...•••• 
Mathieson,  Electric  Automatic  Mines 
Mathieson,  Circuit-Closer   .... 
Mathieson,  Signalling  Apparatus 
McEvoy  (Captain),  Circuit-Closer 
McEvoy  (Captain),  Signalling  Apparatus    . 

Mefford,  Air  Gun 

Melenite 

Mica  Powder 

Mine  Blocks 

Mooring  Gear 

Mooring,  Single  and  Double 
Mud  Craters,  Experiments 


207 

122 

134 

127 

135 

243 

44 

42 

172 

89 

64 

13 


New  York,  Suggested  Mine  Defence 179-183 

Nitro-Glycerine  ._ ^~ 

-•'      '■'■''':':£ 


Nobel  Explosive  Company  . 
Noble  (W.  H.,  Captain  R.A. 
Nordenfelt  Torpedo    . 


254  Index. 

PAGES 

Oberon  Experiments 4,  7 

Observation  Mines 77 

Packing  Ground  Mines 82 

Patrick  Torpedo 233 

Percussive  Automatic  Mines 205,206 

Personnel  for  Submarine  Mining 196 

Photographs,  Experiments  .........  13 

Physiological  Effects  of  Explosions 7 

Picric  Powder     ............  42 

Piles,  Mines  Fixed  to 208 

Plane  Tabling 149-153 

Pola,  Experiments  at  ..........         .  7 

Pressure  Gauges 13 

Rackarock 43 

Reflectors,  Electric  Light 213-216 

Repairing  Faults 194 

Resistances,  Electrical,  of  \Voods 139 

Rise  and  Fall  Mines 69,  70 

Roburite 44,  45,  99 

Rodman  (General  U.S.  Army) 13 

Roth  (Carl) 45 

Ruck  (R.  M.,  Major  R.E.) 69,70,73,99 

Sale  (M.  T.,  Major  R.E.,  C.M.G.),  Electric  Light  Gear     ....  217 

Schonbein,  Gun-Cotton        ..........  47 

Secrecy,  Description  of.  Important 4 

Semi- Advanced  Mines 172 

Shackles 99 

Shore  End  (tables,  P]lectric 105 

Simmons  (General  Sir  Lintorn,  G.C.B.,  &c.)       .....  177,184 

Sims-Edison  Torpedo 233 

Sinkers 19-96 

Sleeman  (Commander  R.N.)        .........  7 

Smith  (Willoughby,  Esq.) 104 

Smokeless  Powder        ...........  225 

Spacing  Electro-Contact  Mines 71 

Spacing  Large  Mines 87 

Steamers      .............  187 

Stores,  Purchase  of .  201 

Stotherd  (R.  H.,  Major-GeneralR.E.) 81,119 

Submersion,  Theory  of 32 

Submersion,  Ground  Mines,  French    ........  10 

Survey,  Mine  Field 190 

Sweeping  for  Mines 211 

Switch,  Klectric 151 

Sympathetic  Detonation 32 

Testing,  p:iectric 156-162 

Thermo-(!alvanometer  ..........         155 

Thomson  (Sir  William) 190 

Tonite 42,49 

Torpedo  Artillery 243-249 

Torpedoes 226-249 

Tramway  for  Depot 166 

Vorsicticheten  Experiments 7 

Vulcan  Powder 42 

Ward  (H.,  Major-Gcneral  R.E. ),  Electric  Fuzes  ....  109,111 

Ward  (H.,  Major-General  R.K.. ),  Thermo-Galvanometer     ....         155 


Index. 


255 


Warner 

War,  Crimean      ..... 

War  of  Independence. 

War  of  Secession  (American) 

Watkin  (Major  R.A.) 

Whitehead  Torpedo     .... 

Wires,  Copper,  Details  of    . 

Wire  Ropes 

Zalinski  (E.  L.,  Captain  U.S.  Artillery) 


2, 
U.S 
•2-26-228 
103 

98 


.243  249 


ERRATA. 


PD        ,  PD 
Page  38,  formula  over  Fig.  19,  for    ,j      read    ^  . 


„  63,  Ime  o'j 
„  64,  line  27  [ 
„    67,  line    6  J 


Table  XX.,  page  60,  is  referred  to. 


„    87,  Table  XXVII.  should  come  at  foot  of  page. 

,,    150,  line  4,  for  "  is  situated  "  read  "  can  be  situated." 

,,    232,  line  11,  for  "  efficiency  "  read  "  inefKciency." 


Messrs.  DAY,  SUMMERS,  &  GO., 

Marine  Engineers,  SOUTHAMPTON, 

Undertake    the   Manufacture    and    Sivp2^ly   of   SUBMABINE 

MINING  BOATS,  STEAMERS,  MINES,  CIRCUIT-CLOSERS, 

and  all  necessary  Machinery,  Stores,  and  Gear. 


Messrs.   ELLIOTT   BROS, 

Electrical  Engineers,  LONDON, 

Undertake  the  Manufacture  and  Supply  of  the  INSTRUMENTS 
and  APPARATUS  required  for  Submarine  Mining. 


'KINTEU  AT  THE  BEDFORD  1-KESS,  20  AND  21,  BEDFOKDBUKY,  LONDON,  W. 

O 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
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